Can you advice me a seinen that you really like?

You can try Shamo. I didn't finish it though.

https://www.mangago.me/read-manga/pigpen/ (just so u know this one's a manhwa not a manga)

https://www.mangago.me/read-manga/zankyou/

https://www.mangago.me/read-manga/jagaaaaaan/

https://www.mangago.me/read-manga/monster/

https://www.mangago.me/read-manga/oyasumi_punpun/ (I'm recommending this one bc it's rlly *rlly* popular and a lot of ppl seem to like it but tbh I don't particularly like it)

https://www.mangago.me/read-manga/ajin/
https://www.mangago.me/read-manga/chi_no_wadachi/
https://www.mangago.me/read-manga/vinland_saga/
https://www.mangago.me/read-manga/dorohedoro/
https://www.mangago.me/read-manga/monster/
https://www.mangago.me/read-manga/tomodachi_game/
https://www.mangago.me/read-manga/20th_century_boys/
https://www.mangago.me/read-manga/kokou_no_hito/
https://www.mangago.me/read-manga/watashitachi_no_shiawase_na_jikan/
https://www.mangago.me/read-manga/mushishi/
https://www.mangago.me/read-manga/the_fable/
https://www.mangago.me/read-manga/liar_game/
https://www.mangago.me/read-manga/blue_period/
https://www.mangago.me/read-manga/sangatsu_no_lion/
https://www.mangago.me/read-manga/blue_giant/
https://www.mangago.me/read-manga/takopii_no_genzai/
https://www.mangago.me/read-manga/piano_no_mori/
https://www.mangago.me/read-manga/pigpen/ (manhwa)

and here's some I haven't read yet but have heard are rlly good:
https://www.mangago.me/read-manga/homunculus/
https://www.mangago.me/read-manga/xxxholic/
https://www.mangago.me/read-manga/shin_ai_naru_boku_e_satsui_wo_komete/
https://www.mangago.me/read-manga/double_noda_ayako/
https://www.mangago.me/read-manga/yuureitou/

and some I haven't read in a long time so I don't actually remember if they were good or not but here you go anyway:
https://www.mangago.me/read-manga/devils_line/
https://www.mangago.me/read-manga/kasane/
https://www.mangago.me/read-manga/me_and_the_devil_blues/

https://www.mangago.me/read-manga/efforts_never_betray/
idk if it's really a seinen, but it's really good

Oki, thanks!!!!

Oh my!!! Thank you so much

Waaaaaa!!!!! Thank you!! Gosh, Monster..you are soo right!

I wacthed Blue Period, didn't read the manga. And Mushishi inspires me alllllot

I read lots of good comments about Vinland Saga

Well, thank youuuuuu

I think I'm gonna like it!! Thank youuuuu