https://www.mangago.zone/read-manga/beware_of_the_villainess/ - 4th wall humour, FL is villainess type, but she wasn't important novel character, so basicaly she's side character and her love interest isn't duke or anything
https://www.mangago.zone/read-manga/i_became_a_maid_in_a_tl_novel/ - side character, orphan maid FL, slow burn, big age difference between her and ML
https://www.mangago.zone/read-manga/seduce_the_villain_s_father/ - FL is original FL sister who wasn't even mentioned in novel from what I remember
The first night with the duke (she was an extra...)
Both BL but this one
https://www.mangago.zone/read-manga/zettai_bl_ni_naru_sekai_vs_zettai_bl_ni_naritakunai_otoko/ is so hilarious that I think it's not even necessary for you to have read BL before.
This one it's more enjoyable if you read the genre: https://www.mangago.zone/home/people/3455178/manga/3/?page=19
Yooo, do yall have
Any manga/manhwua etc that has mc who is a side character?
Or any manga where there is a 4th wall humour