Anti-Hero/“evil” protagonist?

There's a lot of gray area to what you mean by evil so I'm just gonna go for different types of evil

My top recommendation is the webtoon My Deepest Secret. You can find it for free in the line webtoon app and website. Basically about a girl who's boyfriend is a psychopath.

Death Note ofc cause the dude is crazy

This one has a murderer as the female lead http://www.mangago.zone/read-manga/elfen_lied/

I wouldn't say the mc for this one is evil but he's definitely very far from being a hero http://www.mangago.zone/read-manga/kuroshitsuji/

(BL) A killer and a stalker as mcs http://www.mangago.zone/read-manga/killing_stalking/?av=2

(BL) The second seme treats the uke horribly http://www.mangago.zone/read-manga/ayakashi_tsukai_no_yome_sagashi/

(BL) Igen could be evil depending on where you looking at it from. He has the other main lead as a slave. http://www.mangago.zone/read-manga/to_take_an_enemys_heart/

grandmaster of demonic cultivation. It has a webtoon and novel

Uke is a feared evil man of his time.