back below 1200 after 20,000 + games and can’t win any games at this level.
Some say openings just postpone the start of the game, and to study tactics. But openings are not normal tactics. They all branch from the same position, making it worth learning. And there are opening traps people can set, and a much smaller number of them than middle game traps, making it worth learning them, or their themes.

What time controls are you playing?
My bullet and blitz ratings are volatile but my rapid rating is steady in my case.

My first piece of advice is don't be a smartass when you ask for help and someone takes the time to comment on your thread to try to offer advice or help.
Since I don't like your attitude, how about you figure out, "what gives?".
Take a break and review your games when you were 1500-1600 and see what you were doing back then that you are not doing now.
This has been my fear that someday I will suddenly play way worse than what I usually play because I have seen so many accounts on this website that have their highest rating be 300 points higher than their current rating. Another thing which makes me fear such scenario a little bit is that often I don't really know what I am doing better right now than when I was 200-300 points lower rated.

This has been my fear that someboday I will suddenly play way worse than what I usually play because I have seen so many accounts on this website that have their highest rating be 300 points higher than their current rating. Another thing which makes me fear such scenario a little bit is that often I don't really know what I am doing better right now than when I was 200-300 points lower rated.
If you play a lot you'll get a lucky win streak now and then. Especially if you rematch (someone on tilt loses to you over and over) and you get a really high peak rating... but your real rating is 100s of points lower.
The only thing to be scared of is if you looked at a lot of different user's graphs and they were ____ rating for a long time (time and games), and then dropped.

Yeah it's weird.
Any major changes in your life over the last few months?

Your matches and mine are dominated by blunders and mistakes. Puzzles and tactics can help with that, but perhaps more valuable is to improve blunder checking.

No one has even looked at this person's rating graph. The OP is not asking how to be better than 1200, they're asking for an explanation for their rare situation.
For over 500 games, and across multiple months, the OP went between 1400-1500. Then 1 month and a few 100 game later they're below 1200. This isn't normal.
If two people aren't playing on the account, then my guess is there has been some changes in the OP's life or way they play. For example playing early in the morning when that didn't used to happen, long COVID, playing on a trackpad after a mouse broke, etc.

There are a lot of underrated players at 400, 800 and 1200 due to the ability to pick whichever rating you want to start a "new" account at. Once you get away from these points, you should start smoothly climbing back to your real rating

My first piece of advice is don't be a smartass when you ask for help and someone takes the time to comment on your thread to try to offer advice or help.
If that someone gives a completely nonsense advice, making fun of it is justified. Of course, it might have been better to just ignore it.

long COVID, playing on a trackpad after a mouse broke, etc.
Did you really just cite "long covid" as a potential reason why someone is playing poorly? 🤦🏾♂️ that's a new one
What is a little bit worrying in your case is that your rapid rating never reached 1550. 1500 blitz rating maps to 1650 rapid rating. On the other had, 1200 blitz rating maps to 1400 rapid rating and your rapid rating is in the 1400s (and your rapid rating was in the 1400s when your blitz rating was in the 1500s which is very unusual). If you start to play more rapid games, spend more time thinking about the moves, watch chess content on youtube, analyse your games after you play them, you will get your rapid rating to 1600-1700 and then your blitz rating will naturally get to 1500 when you start playing blitz again. You can still play a little bit of blitz here and there but focusing on a little bit longer games may be what you need since you have played 20k blitz games and that didn't really lead you anywhere. In general, many people don't advise playing blitz for improvement and instead they advise focusing on slower time controls.