Wow that's though to find. Well have you read Ajin? It has an anime as far as I know but it's still pretty unpopular yet extremely good!
Oyasumi Jack the Ripper seems to be pretty decent, I'm not far in though.
Pandora hearts has also an anime but the manga is extremely good and underrated. Idk any other ones rn, have you searched the shounen tags?
I recommend “To Your Eternity”, “Satan 666”, and “Hungry Joker”.
I wish those have animes ┗( T﹏T )┛
black torch
Jujutsu Kaisen
Jigokuraku
I lost my favorites list last year so these are the only ones i remember ╥﹏╥
ability, soul carter and black haze are good too
Please recommend me any shounen manga that is not mainstream (e.g naruto,onepiece,fairytail,dr.stone,kimetsu no yaiba,one punch man,boku no hero,etc) and if still very interesting read that you will not get bored until you finish it. I also hope the mc is overpowered please
Any shounen manga that is underrated preferable doesnt have an anime yet