For Chess, it sounds like you need to improve looking at Tactics and Endgames.
Tactics are looking for specific exchanges that benefit you. I'd recommend https://www.chesstactics.org/ as a great resource for being taught the tactics and being able to recognize them. There's a lot of Chess Puzzles out there on things like chesstempo and lichess. If you can easily recognize and execute these tactics, then you won't lose opportunities to gain serious material advantages.
I don't have a good endgame one on hand. Fundamentally though if you know how the game will end, you can push your game state towards a useful winning position. And it helps make sure you don't give away a game by stupid mistakes.
The next layer on top of that is understanding the strategic choices. Sometimes higher level players will make what seems like a really boring move that doesn't have an immediate effect (doesn't solve or generate a threat), but it help their "position" for the future. Things like placing a rook on the open file, or positioning a bishop/knight on a "good" square.
As for openings, since you're a participant in the game you can pick a main opening line that you like and then dive into it, learning all the typical variations in the book that you might see. For example, someone might offer a Queens Gambit, but you get to choose if you Accept or Decline as Black. So experiment a bit, and if you really enjoy 1.E4 openings, then dive into the variations (and counters for when you're black).
-----------------------------------------------
For music, trust me learning theory doesn't turn you into an academic. It lets you recognize things, but they are merely the bones on top of which you build everything else. It's like Assembly (incoming not-great analogy). Sure you can program without ever getting into that. I have a musician friend who never got formal training and he's doing just fine and actually has a great intuitive ear and sense of the music. But the moment he learned Theory, suddenly everything clicked because he had the underlying bones for all of his intuitions he's build up over the years and can communicate them in a standard language.
I don't have great resource on-hand. But just dive into learning the theory alongside playing a lot.
Tactics are looking for specific exchanges that benefit you. I'd recommend https://www.chesstactics.org/ as a great resource for being taught the tactics and being able to recognize them. There's a lot of Chess Puzzles out there on things like chesstempo and lichess. If you can easily recognize and execute these tactics, then you won't lose opportunities to gain serious material advantages.
I don't have a good endgame one on hand. Fundamentally though if you know how the game will end, you can push your game state towards a useful winning position. And it helps make sure you don't give away a game by stupid mistakes.
The next layer on top of that is understanding the strategic choices. Sometimes higher level players will make what seems like a really boring move that doesn't have an immediate effect (doesn't solve or generate a threat), but it help their "position" for the future. Things like placing a rook on the open file, or positioning a bishop/knight on a "good" square.
As for openings, since you're a participant in the game you can pick a main opening line that you like and then dive into it, learning all the typical variations in the book that you might see. For example, someone might offer a Queens Gambit, but you get to choose if you Accept or Decline as Black. So experiment a bit, and if you really enjoy 1.E4 openings, then dive into the variations (and counters for when you're black).
-----------------------------------------------
For music, trust me learning theory doesn't turn you into an academic. It lets you recognize things, but they are merely the bones on top of which you build everything else. It's like Assembly (incoming not-great analogy). Sure you can program without ever getting into that. I have a musician friend who never got formal training and he's doing just fine and actually has a great intuitive ear and sense of the music. But the moment he learned Theory, suddenly everything clicked because he had the underlying bones for all of his intuitions he's build up over the years and can communicate them in a standard language.
I don't have great resource on-hand. But just dive into learning the theory alongside playing a lot.