In my role as a GM for a SR5 group i often have the problem, that the decker in our group is not in the field with the rest of the team, which is perfectly fine. But after the fact complains, that he is bored, while the action happens inside the complex he decided to stay out of.

Since his character is definetly not suited to join in on any longer shoot-out or physically demanding tasks in general. I feel uncomfortable with the idea of forcing him to go inside along with the group.

Therefore I am facing the problem of presenting him with a more or less meaningful and reasonable task in the mean time.

And by the way, he is so good at what he does, that most if not all security measures that their target has in the matrix, are disabled before the team ever arrives at the target location. Although this should not imply that he is sitting home alone kilometers away, since that would be impossible considering Noise.

So either I suprise them with a late shift decker that reboots the system once in a while, to undo all the deckers work (which would seem kinda unfair to me), or I accept that he has nothing to do in the mean time.

This answer comes down primarily to "What about..."

Noise?

This is the biggest one

Why is your Decker not in the field? The ability to hack the stuff in the run location requires that he get in close physical proximity to it. That's how the SR5 Matrix works. The whole "I'm a Decker who sits and home and does all my work remotely" doesn't fly in SR5, because of the Noise mechanics. The further you are from something and the more stuff is in between you and the thing you're trying to hack--the bigger penalties you take to trying to hack it. Any site worth their salt knows this and would set up countermeasures (like walls, Em-blocking paint, landscaping, a Faraday Cage, or just by putting important things away from the exterior of the building) that prevent someone from hacking into their stuff from outside the building.

In short...in SR5, a Decker can do some work remote--such as setting up fake IDs or getting blueprints and so on...but they can't mess with the cameras, control locks, disable security systems, shut the alarm off, break into a computer for a datasteal, or anything else like it without being with the team breaking into the building.

And that's not to mention that some security systems, data repos, etc. are offline and thus cannot be accessed without a direct physical connection to that thing.

And no, 'routing' through a friend's commlink doesn't work, because you get all that Noise trying to connect to them, too.

Tactical Support?

Does your Decker not realize how useful they are in dealing with other sorts of obstacles?

• A goon with a giant Smartgun is a lot less scary if his Smartgun gets bricked.


• A Decker who takes over the Cameras or security sensors can provide live-intel to the party


• If the alarm goes off, the ability to fake where the alarm says intruders are can buy you time, or fake a false-alarm message


• Drones are much less scary when the Decker keeps subverting or Bricking them


• Whoops, did that massive cybered up troll forget to turn the wireless off on his Cybereyes? Guess he only gets to see what the Decker wants him to see.

DataSteals?

Probably the most common job in the SR world is the datasteal...get in, get your Decker close to a secured data repository, then let them hack into it and steal it. Because of the Noise issues mentioned above, the Decker must by with the team because otherwise he would be operating at something like a -200 dice pool.

Other Skills

Deckers, by necessity, have high Logic. This also makes them well-suited to be good at any of the Mechanic skills, as well as Medicine and Demolitions. Any of those skills can be useful on the actual run...especially if no one on the team has those skills.

The ability to cleanly sabotage a piece of tech requires that you be able to understand that tech and know how it works...Smashy the Street Samurai can break the thing, but sabotage that makes it look like it failed on its own requires skill in working on the thing you're trying to sabotage.

Summary

This doesn't seem like a DM-style issue to me. If I had to guess, you're ignoring the Noise rules, and that's what is causing this issue...if the Decker doesn't have to go with the team to do their job, then of course they are going to do it all remotely then sit safely at home. That's kind of the whole point of the Noise rules--force the Decker to actually go on the run with the rest of the team

Make the current strategy unworkable or very difficult.

It's easy to lose sight of this when working with a TTRPG, but it's important to bear in mind that the rules don't describe the setting but rather that the setting suggests certain rules.

I'll expand on what that means in the context of Deckers in SR 5e:

• Deckers are relatively common, both the legal and less-legal varieties


• Physical proximity is a factor in penetrating secure data areas


• Data is generally valuable


• Data held by a target worth stealing from is likely to be very
  valuable


• A target worth stealing from is likely to have nontrivial resources


• A target worth stealing from that has data worth stealing probably
  understands what Deckers can do pretty thoroughly, and the Matrix more broadly

If we put those together we will have trouble avoiding this conclusion: No place or organization the team is targeting would fail to have security in place anywhere a Decker might operate against them. If a Decker can do something of consequence within 100 meters of the target location, then security measures will apply to the area at least 100 meters around the location in all directions.

It should be effectively impossible for the Decker to both be close enough to the target area to work effectively and also be reasonably safe from various security measures. If the Decker goes on a run, they are in danger whether they're with the rest of the team or not. They may even be safer with the team, since they'll have backup and support to face the inescapable dangers.

The Decker might want to put some Karma into specific skills to deal with that, even if it means that they can't quite ultra-specialize as much. They don't have to be soldiers, but they do need to have some way to avoid being seen or attacked. Alternatively, the rest of the team might need to devote some extra effort to protecting their Decker to achieve even minimal success.

Ignoring security measures in this case is similar to having the team go on a run but declaring that there simply aren't any guards or defenses. Of course there would be less to do in such a case, because most of the things the party would have to deal with have been arbitrarily, entirely removed.

I also noticed this:

And by the way, he is so good at what he does, that most if not all security measures that their target has in the matrix, are disabled before the team ever arrives at the target location.

This suggests to me that the Matrix portions of the runs are too easy for this character. The Decker's skill must make these obstacles trivial for them to be completely defeated before the rest of the team even arrives at the site. That's a problem that transcends PC class, build, or skill. The natural fix for that would be to make the Matrix sections more challenging-- harder success thresholds on skill checks, more security spiders, more observant GOD, and so on.

If you decline to add security measures that can frustrate or endanger the Decker, allow the Decker to be so much better than their adversaries that the obstacles they face are trivial, and do not include challenges for which the Decker is not already specialized then of course there will be nothing for the Decker to do. Those are where most of the game is, outside of character building.

Create urgency

You say that he has disabled everything before the team even arrives. I think we can agree that this should never happen. One thing is spatial proximity, i.e. that he has to be on site to work. The other answers already covered that point, but you seem to be very cautious about that. There is however another proximity that is equally important and this is closeness in time. There are so many fun reasons why hacking can only take place at the last second, let me just sketch a few ideas:

1. You already mentioned the late shift decker that resets the system. Don't make it a surprise, instead make sure that they know he's there. But he cannot work 24/7 so at some point there is a shift change. The dynamics are immediately different if your whole team only has an uncertain amount of minutes for the whole thing. As soon as one layer of defense is down, and your team is on the move again your decker has to already work on the next. If either are to slow or make a mistake, they suddenly face two enemy deckers sounding the alarm and trying to undo all the work.




2. You cannot hack what is not running. In a world where deckers are a constant threat, there is no reason to present them with to much attack surface. So obviously the automatic defense cannons are powered down when not in use. Only when your team crashes into the door will the security guard press the button starting the boot-up sequence. Better shut it down again fast.




3. You cannot hack beforehand what you do not know about. Couples well with the other ideas. If defeating the outer layer of protection reveals you five minutes later, or the system only boots when you enter the door, your decker will have to improvise, because he cannot know what to expect.




4. You cannot hack beforehand what you didn't know you had to hack. Hacking that access hatch to the sewers is trivial, any defences horribly outdated, only there to keep out vagrants, essentially scriptkiddy's first run. No DM would ask you to even roll the dice. But when exit plans A-F fell through and your team is stuck there, getting shot at from all sides, there is still a difference between being able to do it in a minute or in 5 seconds.

To keep both sides interested you should interleave the action. In combat this is easy, with the decker just taking turns like everyone else. But also out of combat you can do similar things. Your team clears a physical obstacle, then your decker a digital one, then back again and so on. Just like in any good heist movie those actions always seem to take up the same amount of time and sync magically. And if things still threaten to get out of order simply adjust. If the decker is taking to much time, give the others a few more goons to shoot at in the meantime. If he is to fast, boot up another unseen surprise system to counteract. Your main goal is not to follow a strict script but for all players to feel valuable parts of the action and have fun.