Please recommend me some manga about: 1. Youkai 2. Criminal/detective/problem-solving man...

Kyouko Suiri

https://www.mangago.zone/read-manga/kyokou_suiri_invented_inference/

Kusuriya no Hitorigoto (medical historical)
Be blues(soccer)
Ao ashi(soccer)
Big wind up( baseball)
Kaiju no 8 (monster extermination, Shounen)
Mashle: magic and muscles (very hilarious)

This one is about yokai and detective investigation kinda thing.

kemono jihen

1. Youkai: https://www.mangago.zone/read-manga/youkai_gakkou_no_sensei_hajimemashita/
2. Criminal/Detective:
https://www.mangago.zone/read-manga/ouroboros/
https://www.mangago.zone/read-manga/yuukoku_no_moriarty/
https://www.mangago.zone/read-manga/kuroshitsuji/
https://www.mangago.zone/read-manga/shinrei_tantei_yakumo/
https://www.mangago.zone/read-manga/kamonohashi_ron_no_kindan_suiri/
3. Maybe you’ll find some underrated stuff you’d like here: https://www.mangago.zone/home/mangalist/1178133/

Jigoku Kurayami Hana Mo Naki literally one of the best I have read :P