It's exactly what you said, she seems to can't accept the fact you can make your own decisions and have your own opinions. I don't know the full story, but your feelings are real here and is valid, it's weird indeed to always disagree on things on things she seems will agree on. It can feel controlling of the situation and she's losing that power over you. So stay strong, what you feel matters too.

i feel like my mom just can't accept the fact that im now a full grown adult who is capable of making reasonable decisions and opinions. im starting to see a pattern of me voicing an opinion that i thought my mom would agree with, because, i get it from her, but then she would just disagree because..???
she just can't not fucking argue with me it's either she's right or im wrong(?) like what's up wit that why does she do this i really don't understand what's going on in her head. is it just a reflex to just refute everything i say, just for the love of the game?