idk about underrated but try these:
https://www.mangago.me/read-manga/a_declaration_of_revenge/
https://www.mangago.me/read-manga/hell_high_water/
https://www.mangago.me/read-manga/shall_we_go_surfing/
https://www.mangago.me/read-manga/what_s_your_name/
https://www.mangago.me/read-manga/love_me_dramatically/
https://www.mangago.me/read-manga/swallow_gawee/
https://www.mangago.me/read-manga/until_i_meet_my_husband/
thank you so much bestieee
https://www.mangago.me/read-manga/back_in_time_to_you/
https://www.mangago.me/read-manga/not_for_the_faint_of_heart/
https://www.mangago.me/read-manga/lifeless_man/
https://www.mangago.me/read-manga/tonari_no_metaller_san/
https://www.mangago.me/read-manga/sonna_me_de_mite_kure/
https://www.mangago.me/read-manga/my_childhood_friend_was_a_god/
https://www.mangago.me/read-manga/spring_snow_odongtong/
https://www.mangago.me/read-manga/sasaki_to_miyano/
https://www.mangago.me/read-manga/kimi_to_no_dogfight/
https://www.mangago.me/read-manga/itonaga_kun_no_koi_no_ito/
https://www.mangago.me/read-manga/shuchu_ni_otoshite_iidesuka/
https://www.mangago.me/read-manga/a_b/
https://www.mangago.me/read-manga/guardian_with_benefits/
https://www.mangago.me/read-manga/park_hanhoo_s_manager/
https://www.mangago.me/read-manga/timeless_melody/
https://www.mangago.me/read-manga/tu_quoque/
https://www.mangago.me/read-manga/daniel_s_extremely_private_villain/
hii can u guys please give me underrated bl manhwa