Apple Id Issue, please help

I've changed the email address for my apple id a few months ago and had no issues with it. Today, I was trying to do a factory reset of my M1 macbook and encountered a really weird issue. I am being asked to enter my apple id credentials, but it shows me my old email for some reason? And it doesn't accept neither old nor new password for it? I was able to reset my mac using the device password, but now I am not sure what to do in the long term. Will my mac always be attached to that incorrect apple id now? Can it be somehow disconnected from it? And even if apple id was correct, what if I decide to sell it in the future, will I have to give away my apple id to another person? This doesn't make sense.