How to counter a very theoretical opening?

It depends on which opening you are having trouble against different openings different solutions.

if someone plays something you don't know, they can't follow theory. for example, if I as White play the Delayed Alapin Sicilian line

and you don't know how to respond to it and just keep playing normal developing moves, White can't follow theory and will be forced to also play normal developing moves. Theory is twofold: white plays a theory move, then black plays a theory move, and so on until you leave theory. If Black doesn't play a theory move, however, usually White's next theory move is no longer the best move and so White is forced to adapt on the fly, same as you are.

The "Without spending so much time" is a you problem.

The only way to resolve your issue is to bite the bullet and spend time analyzing lines you can face, even if you don't enjoy them.

A Sicilian player cannot only prepare their favorite open Sicilian line. You also must be prepared for the Alapin, Morris, Closed, Grand Prix, etc. A French player not only needs to know the Advance, Tarrasch, Exchange, and 3.Nc3. He must also know the Two Knights French, 2.b3, KIA, etc. A Petroff player must know Bishop's Opening, Danish, Center Game, King's Gambit, Vienna, and either the 3 or 4 knights.

Get out a real board with pieces and study rather than wasting your time here.

Tactics is knowing what to do when there's something to do.

Strategy is knowing what to do when there's NOTHING to do.

Need a few tips on strategy? Try reading this:

GM Larry Evans' method of static analysis - Chess Forums - Chess.com

Read my post #4, #'s 7 to 10 and especially post #12. Then play over the three sample games, reading the notes to the moves.

If you have questions, you can ask them in that thread.

^^ Exactly this.

Get a collection of "best games in chess", for example the Mammoth one, but there are others. Take your time, play through all the games. You will learn a lot.

But what about openings? Well, there will be games in openings you don't play, or in openings you do play but not that way. This is a _good_ thing. Now you get ideas about how to play widely varied positions. Next time your opponent goes out of book maybe you can borrow an idea from a different opening.

play the london

At your level, it's extremely unlikely that you'll encounter anyone with deep knowledge of any opening. So the first thing is don't worry about it. Second, develop, get your king to safety, make moves that control the center, attack weaknesses in their position, eliminate weaknesses in your position. Easier said than done, of course. Which is why improving in chess requires serious study.

All three of them are very valid concerns for someone rated 2200+. At your current level, they are nothing to worry, or even care about.

All you have to do right now is not blundering your pieces, and spot what your opponent has blundered. Just develop your tactical vision and skills, and you can care about the rest later.

Also, you should not worry if you fall into an opening trap. Even if you eventually lose the game, the next time you will meet the same trap you won't fall for it.

So, you do not do analysis. You let an engine do that for you, and this isn't productive.

The right way is analysing a game without external aid, and only after doing so using an engine or whatever to see where your analysis is wrong. Else, you are using passive mode analysis, which does not work for most people.