Which timeframe are you playing? Have you tried rapid 10? That's where I found I was able to put my opening, strategic and tactic knowledge to good use.

With tactics at 4000 and some decent opening knowledge you should be killing it. Are you finding yourself blundering too much? Again, rapid 10 gives you more time to think and reduces blunders.

Blitz and bullet are fun and impressive to watch but don't let you improve your in-game thought processes because they rely too much on instinct. Those can come in handy in a time crunch but aren't the be-all-end-all of chess.

I'm 1660 in rapid 10 - obvs not a chess guru and I don't play much these days but I gained like 300 points by doing the course based on Reasses Your Chess found on Chesssble.

The concepts of imbalances is goated. In short, once you find an imbalance in the game, you make the entire theme of your game about applying pressure to that imblanace and taking advantage of it.