Idk what to say. Just stop playing so much chess when you are tilted. If you are unemployed it's best to use that time into learning a useful skill which could potentially land you a job. Chess should only be a small part of your life.
Stupid feelings

Everyone has there ups and downs. Once I had a 10 game losing streak in blitz. The next day I got to my highest rating in blitz. You shouldn't let some loses get you down. Every loss has there good side if you know how to learn for them. If you fell like you just keep losing then take a break and solve some puzzles.

First…get out of Serbia.
Solid strategy, except not everyone can afford that. I have enough chaos on my plate as it is, but I have considered that before, and I wouldn't just rule it out. I just have more stuff to fix where I am, instead of running from it.

Idk what to say. Just stop playing so much chess when you are tilted. If you are unemployed it's best to use that time into learning a useful skill which could potentially land you a job. Chess should only be a small part of your life.
Without going too in-depth, I agree, but the search is going opposite of smoothly, unfortunately enough.

Everyone has there ups and downs. Once I had a 10 game losing streak in blitz. The next day I got to my highest rating in blitz. You shouldn't let some loses get you down. Every loss has there good side if you know how to learn for them. If you fell like you just keep losing then take a break and solve some puzzles.
I did go to solve puzzles, and then I lost 84 points of rating on TWO SLIPS... like, physical slips, which were very unfortunate. I didn't even have click&drag enabled, I tapped on the piece then on a different available square (as always), and I seriously don't even know how I managed to mess it up.
Doesn't mean that my understanding and/or vision is worse, given that I knew the solutions; it's just that I'm annoyed that my rating doesn't exactly reflect that anymore, due to dumb stuff which is gonna take me hundreds of correct answers only to annul.

OP has played 153 games in 10 years with no recent rapid games
OP plays on Lichess, I find that very interesting.

Here to vent once again: recently I lost two games to endgame blunders, which made me realise that my main problems are 1) not seeing tactics, and 2) not having the technique to convert advantages. I should feel good about getting to know what my weaknesses are, but alas, I have no clue on how to train myself optimally. Should I go through puzzles by various themes (and which ones should I choose first?), or should I instead go through Lichess's "healthy mix" from the easiest difficulty to the hardest? It's very frustrating, to be honest, and I keep beating myself up for losing won games so much. It's beyond disheartening to think of myself as so incompetent... and again, if I get too serious, I'm gonna get obsessed again, and I don't want that, either.

Maybe study some endgames and also do some puzzles.
Well yeah, I just gotta figure out how to go about doing puzzles. I don't have a strategy for learning tactics. xD As for the endgames, I've got enough instructive materials as it is, so I'm not worried about that.
Here's a different take, though: lately I've been feeling extra bad about my losses because my mood's been lower than usual in the last 10-20 days, and that's without chess. Not sure why that's so. Might be seasonal (cold weather, diminished sunlight... just winter things, essentially), or it might be something else that's not entirely clear to me as of this moment.
Either way, while a good game can improve my mood to an extent, a bad game can send it plummeting that much more. It's not chess, it's me. I'm trying to use it as a coping mechanism, but it's been backfiring on me so far, even if I am learning something along the way.
Ever come to a point at which you fully realise you're on tilt (upon losing a chess game) and it kinda makes you feel less tilted as a result, but then you keep feeling like you're at a loss as to what to do with those emotions, questioning whether or not they serve any purpose in your life whatsoever?
I'm experiencing one of those moments as I'm writing this. Without going into detail about what made me tilt (a couple of rapid games, as well as two puzzles botched by fingerslips/mouseslips), as someone who finds meaning in gradually improving as a chess player through methods of his own choosing, I feel like there's no point in feeling bad about the loss of my rating points... but since I still feel bad, it's like I'm being wasteful with my feelings.
I remember Hikaru Nakamura saying many times that the negative emotions which result from losing chess games should be channeled into chess improvement, but I don't think I can afford that. If I truly went about doing that, I'd get obsessed big time. I already used to be like that so much that I had to tone down to playing a couple rapid games a month in order to try to keep it as fun and undevastating as possible.
How should amateurs who don't consider chess their vocation go about it? I just wanted to get out of a slump because it's a depressing winter here and I'm unemployed and I need to unwind and occupy my mind with something that stimulates me without stressing me out any further as I go about trying to organise my life and regain some positive feelings, but apparently, even chess puzzles are against me today.