Chess Improvement for a 2000+

I've been around 2000+ for more than 6 months now (with occasional ups and downs). Never read a book, nor studied any openings or endgames nor middle game strategies and only played blitz and bullet primarily. I've seemed to plateau now and can't go higher just by playing blitz. I play only e4 as white, don't really have anything good to respond to c5 (tried both open and closed Sicilian but always end up in a bad position out of the opening). And as black I only play the petrov in response to e4, Englund gambit (lol) and QGD against d4. Can anyone suggest what to follow to improve from here, more so, how to study openings or books??

against sicilian - grand prix attack
learn some other openings and study from books and watch content from youtube.
I'm learning the pirc and play vienna,

#1
Do not worry about openings.
Closed Sicilian, Petrov, Queen's Gambit Declines are all fine, but I would ditch Englund Gambit.
If you want to progress, then play rapid or classical.
Use all the time allowed by the time control. Time is a resource, use it.
Whenever you lose a game, stop and analyse it first.
Maybe study Capablanca's "Chess Fundamentals".
Or study an endgame book.

Englund gambit because, very much used to playing e5 to e4, so in fast games I would premove e5 and if white has played d4, it turns into Englund gambit. Know a couple of traps there but its not really my go to opening

also you are already quite strong. That mean effort needed to get stroger gain additional 100 pts if far higher that it was from 1900 to 2000.. Every one will eventually plateu

If you want to progress, play rapid or blitz games, rapid usually preferred, and after the game, regardless of the result, analyze it. Analyzing games can show you certain tactical patterns and some positional ideas.

as #2 said, play grand prix against sicilian; it's aggressive and extremly useful in all time format (bullet adn UB included). PLay slow games (at least 30+20). Analyse your gamesn even if you won. Don't let yourself down. If you play quite regularly (like almost everyday) you will still improve and could well reach 2500 if you practice hard. Have a look at some master games (i like agadmator) and try to grasp the ideas behind their moves. PLay against an engine and try to comprehend his moves (why did he push b4 instead of recapturing the bishop ...). I'm totally against the fact that you've "reached a plateau" and then won't improve much. Just play regularly, do tactics and learn aggressive openings (that the best thing to do in blitz) and don't waste time in the opening section, moves should be automatic (like 20s for the opening max). Hope you'll reach 2500 soon enough ;)

Study Endgames Seriously. I recommend Dvoretsky Endgame Manual (Sorry Silman fans). My classmate 30+ years ago become a National Master within few years after seriously studying the book.

Exactly what @ryan121 suggest,, Dvoretsky's Manual is pretty much the best. I stopped studying tactics in favor of endgame studies, I'll say endgames improve your calculation more than basic tactic puzzles. And it's not just Dvoretsky's Manual, everything Dvoretsky writes is worth reading, especially if your are a 2000+ improving player