I still get my mail at my parents house (just haven’t changed my address)

So every time I get mail my mother opens it and fails to tell me I even had/have mail until I see an OPEN envelope somewhere with my name on it that I haven’t seen.

She always says, “oh it said this on it so I just peaked in it” and never remembers when it came.

I’ve told her not to open my mail and apparently she “forgets”

My mother and I do not have a relationship, she is narcissistic and bipolar, and several other things. I know I should just change my address obviously it would solve this but why the hell does she feel the need to open my mail? Like is that a thing?