I would like some shounen and seinen mangas which are not so popular but still interesting...

I have a lot of yaoi and shoujo

Anyway try killing stalking it's my favorite cz I have just animes in psycho

http://www.mangago.me/read-manga/spy_x_family/
http://www.mangago.me/read-manga/musubaru_yakeato/
http://www.mangago.me/read-manga/i_will_die_soon/
http://www.mangago.me/read-manga/disease/
http://www.mangago.me/read-manga/coffin_jackson/
http://www.mangago.me/read-manga/ageku_no_hate_no_kanon/

I have three different recommendations just if you want to give them a try ^^

Uncanny Brains is very good: girl finds a mysterious boy and they end up in some kind of conspiracy
http://www.mangago.me/read-manga/uncanny_brains/

Seishun X Kikanjuu: toy guns and survival games + breaking gender roles
http://www.mangago.me/read-manga/seishun_x_kikanjuu/

Fukigen Na Mononokean: chillest manga about exorcisms
http://www.mangago.me/read-manga/fukigen_na_mononokean/

I have read spy x family and enjoyed it a lot, thanks for all your recommendations, I will check them all since I won't be getting out soon (=・ω・=) Thanks a lot

I watched seishun x kikanjuu's anime but I didn't know there was a manga adaptation of it! Thank you! I will check them all (=・ω・=)

I read it and tbh I would rather not read it again, I suffered a lot while reading it ╥﹏╥ Still thanks