https://www.mangago.zone/read-manga/mononobe_koshoten_kaikitan/
https://www.mangago.zone/read-manga/jinrou_game/ (kinda romance but the sequels eventually have none)
https://www.mangago.zone/read-manga/unhinged/ (I think this one fits ur description more)
https://www.mangago.zone/read-manga/noah_of_the_blood_sea/
https://www.mangago.zone/read-manga/massacre_happy_end/
Body electric
aku no kyoten
king's game
boku dake ga inai machi
interview with a murderer (yaoi no romance)
the perfect relationship (yaoi no romance)
ouroboros (kanzaki yuuya)
change the world (kanzaki yuuya)
funouhan
hell dogs
Oooh thank you! These look really interesting!
Looks really cool! I’ll read it!
Any mystery/murder webtoons without romance? Can be manga too, but preferably a webtoon! :) thank you!