stuck at 2100 fide

Don't know the situation in Germany but go to some tournaments where players might be overrated - common tactic/secret for FM's IM's who want to achieve "easy" norms/rating they even travel all whole europe for specific tournaments. Aman last year went to Spain for one specific tournament but failed.
Have you consider reading books by Dvoretsky? Try book like Chess Lessons by Vladimir Popov. Popov produced masters, ims and gms.

lol,funnily enough i had the same problem.Was stuck at 1800 for over an year and now im 2200 .I dunno how it happened,all my hard work just paid off I guess.Don't lose hope,you hit a wall for a while and then seemingly suddenly shoot up.Has happened to a lot of people.Just keep working on your chess.That is the most important thing.1 thing I would suggest is to play in Spain.I played 4 tournaments in Spain this year and realized that Spanish and South American players are highly over-rated compared to Indian and Chinese players.

But I can suggest 2 things
1) Keep study the openings. You are on the right way. You can solidify your repertoire by playing a lot of blitz games. This make you learn about your openings very quickly.
2) Work out on lost games. Both OTB and online. I know it's boring to do but that's exactly what your weakness is. Try to find the real cause. As long as you learn new things, that is a guarantee improvements!

Three types of people will read your post:
1) Those who would be jealous of you (the great majority...);
2) Those in a similar situation (stuck anywhere between 1900 and 2300) - these will either feel your pain, or give you the kind of general advice that didn't really get THEM to the "rating stratosphere";
3) Those who would be able to help by giving you the kind of close attention that will, over time, actually boost your playing strength - and who will most certainly do so for a handsome fee...
Just saying :-)

3 years ago I achieved m first fide rating of 2049. Now it is about 2060 live rating.
I train about 4 or 5 hours a day, the biggest part studing openings, as that is my biggest weakness. I also have a coach.
But I am just not improving.
Has anyone been in a similar situation and knows what the problem could be?
No idea what your problem is, but if you have a coach and don't improve under his guidance, I would suggest trying with another one

Whatever you are doing in your games has to be discovered and improved upon. Find out why you lose in key games and you will start to progress.

identify the next rating level you want to achieve, say 2200 and make like a bat of hell to get there.

I have been in the same situation. Thirty years ago I stalled a little way short of the BCF equivalent of 2200. Now I am back below 2000 (1977).
I expect many other players here have been in the same situation . But none of us knows enough about you to tell hyou for sure what you need to do to improve further, and I doubt that any strong players are going to bother to study your games to figure out what you need to do next ... unless you pay them for the service.
You are going to have to figure it out for yourself, maybe with the help of a coach.
As to whether your failure to improve is your coach's fault, again no-one here is in any position to make such a judgement.
One thing I will say. In all pursuits it can often seem that you are working hard for little reward, but if you persist you eventually break through to a higher level, and when it happens it is sudden, and the improvements are huge. So if you are sure that you are doing the right things it is worth persisting.
But you say you spend most of your time studying openings. That might be the problem. Chess teachers have always told us that it is more important to study other aspects of the game, endgame, attacking methods, pawns structures and the plans associated with them, typical combinations and so on. Maybe you need to start spending time on these and, if necessary, make it up at the board in the opening.
Just because chess professionals spend most of their study time on openings does not mean that it is the right way for lesser players to work. The elite are already very good in all aspects of the game. They already know much that you still need to learn.
When you step back and think about it it is pretty silly for chess players below master standard to emulate the training of top players. I mean would you try to start weight training with the kind of work that an Olympic weightlifter does? Or would you work at learning to play piano in the the same way that a copncert pianist prepares pieces for recital. Well you would quickly find that you just cannot even move the weights gthat the super-strong throw arounbd with ease, and fortunately for aspiring pianists that still struggle to read a written score and cannot play scales and arpeggios very well it is not even possible to practice in the same way as the pros.
Such considerations do not apply to chess. It is very easy to waste your time studying things that are not going to help in the long term, or that you are not yet ready for.

In his book Amateur to IM, Jonathan Hawkins describes how he gained rating (and titles) by switching to endgame study. I'm just a beginner, but who knows, this may help you. Your weakness in openings may not be the real problem?

Many adults players are stuck at some level, mostly 1600-1800. And when we look at younger kids, we are so jealous.. it's so unfair.. i mean how an earth a teeneger is making so much progress for so little time, you beat him at chess, but whole game you strugle, and 3 years after that he becomes NM... and you are at same level .. is just crazy. Its like you have wasted all that time on chess while he made it way higher than you, while finishing school/university at the same time. It's like no problem for them.
It helps to play tournaments often to find your weakest area.
You may be least knowledgeable about openings, but that doesn't mean openings are the weakest part of your performance.
Many adults players are stuck at some level, mostly 1600-1800. And when we look at younger kids, we are so jealous.. it's so unfair.. i mean how an earth a teeneger is making so much progress for so little time, you beat him at chess, but whole game you strugle, and 3 years after that he becomes NM... and you are at same level .. is just crazy. Its like you have wasted all that time on chess while he made it way higher than you, while finishing school/university at the same time. It's like no problem for them.
Sometimes kids are easier opponents because they generally make more unforced errors (not tactical errors, but all other kinds that give you an easy position)... I guess it depends on the position though.

Three types of people will read your post:
1) Those who would be jealous of you (the great majority...);
...That's me, who'd complain about being 2100?
3 years ago I achieved m first fide rating of 2049. Now it is about 2060 live rating.
I train about 4 or 5 hours a day, the biggest part studing openings, as that is my biggest weakness. I also have a coach.
But I am just not improving.
Has anyone been in a similar situation and knows what the problem could be?