Shoujo.
The story starts with a baby fl which is pinknhaired. I think she reincarnated. She has a black haired brother, i think she is planning to get close to him bcs 1st-Theyre not really related by blood and 2nd- i think the bro will become a bad person in the future. In short she wants to be in his good side.
I think it's either one of these:
https://www.mangago.me/read-manga/the_precious_sister_of_the_villainous_grand_duke/
https://www.mangago.me/read-manga/i_will_seduce_the_male_lead_for_my_older_brother/
both matches the description you gave
Historical. The ML crossdresses (long white hair, i think his eyes are red) and drinks potions to look like girl. He has a personal maid who takes care of him but not aware that he's a dude (the maid has black hair) and he falls in love with the maid. Kicked out from the mansion, she lives alone and then one day theres this dude outside her house who has white hair and red eyes like her lady. The dude said he was the lady she is talking about. There 2 other guys tho.
Additional info: i think she was isekaid, the story was supposed to be a love triangle between her lady and the 2 dudes.
Help me find this
SAVE HIM NOWWWWWW