These are the things i care the most: I want a smartphone i can repair on my own (battery and screen are the essential parts), with a bootloader easily unlockable, even better with verified boot / supporting a custom OS with re-lockable bootloader.

I don't care if it's supported by an official foundation or by custom ROMs foundations, i want something that will most likely get the longest term updates and security patches.

Does a device like this even exists?

I know that probably one of the few alternatives here is the fairphone, however it's really expensive and i've read many negative reviews of it (pieces staying out of stock for months or stuff like that), and i can't see the meaning of having a repairable smartphone if i have to spend the same money that i would spend buying 3 smartphones with the same specs that would last me the same time. That said, i know the market isn't favouring these kind of businesses and these devices NEED to be expensive in order to keep existing, but i would like to know some other possible alternatives that satisfy these requirements, if they even exist.

Honestly i've come to a point i would probably prefer spend my money on a guitar instead that on a smartphone and just give up, the industry is terrible 😅