Can someone recommend: FL who's hiding her identity as a boy and/or FL or ML whos hiding ...

Fl who dresses up as a man to hide their identity:
https://www.mangago.zone/read-manga/the_prince_of_myeolyeong/
https://www.mangago.zone/read-manga/my_fair_footman/
https://www.mangago.zone/read-manga/the_villain_discovered_my_identity/
https://www.mangago.zone/read-manga/tokyo_crazy_paradise/
https://www.mangago.zone/read-manga/irregular_empress/
https://www.mangago.zone/read-manga/lady_crystal_is_a_man/
https://www.mangago.zone/read-manga/queen_cecia_s_shorts/

FL who has a male avatar in a video game: https://www.mangago.zone/read-manga/1_2_prince/

This is a favorite of mine, :3.

https://www.mangago.zone/read-manga/the_villainess_cecilia_silvie_doesn_t_want_to_die_so_she_decided_to_cross_dress/
This fits the first thing you wanted

Osora (webtoon)
Mc is born female but was raised and lives as a male for political reasons (doesn't identify as female)

Tyyy youre all the bestヾ(☆▽☆)

Secret identity / power
https://www.mangago.zone/home/mangalist/2086091/
Gender bender
https://www.mangago.zone/home/mangalist/1581724/

Enjoy my dear