I came across this one topic which contained gender bender isekai mangas but i lost it and...

sadly idk which topic you are looking for ╥﹏╥

if you are looking for gender bender or reincarnation stuff there is:

:Hero King reincarnated - the world's strongest apprentice knight:
https://www.mangago.zone/read-manga/eiyu_oh_bu_wo_kiwameru_tame_tensei_su_soshite_sekai_saikyou_no_minarai_kisi/nbt/mpn_chapter-2194506/

:This Girl is a Little Wild:
https://www.mangago.zone/read-manga/this_girl_is_a_little_wild/
(a lot of people confused her previous body to be a guy so maybe its the one you were looking for?)

:The Way That Knight Lives As a Lady:
https://www.mangago.zone/read-manga/the_way_that_knight_lives_as_a_lady/
(same case as "This Girl is a Little Wild")

:Death Is The Only Ending For The Villainess:
https://www.mangago.zone/read-manga/death_is_the_only_ending_for_the_villainess/
(kinda like Trash of the Count's Family because they are reincarnated in similar situations)

:The Villain Discovered My Identity:
https://www.mangago.zone/read-manga/the_villain_discovered_my_identity/
(kinda the opposite, where a girl has to pretend to be a guy.)

:Queen Cecia's Shorts:
https://www.mangago.zone/read-manga/queen_cecia_s_shorts/
(same case as "The Villain Discovered My Identity")

sorry if I couldn't be much help, these were the closest things I could think of (￣□￣)

Thank you eidda!