It's not the same.
But I have a grandma (maternal grandma) like this, and I tried for years and years to be good enough for her.
I have no contact with her now because like your mum she belittles me, insults me and she has a golden balls grandson (my brother)
The last straw for me was when none of them told me my grandad had cancer, I found out through my paternal Uncle who's like my dad, I reached out. My brother then went travelling leaving them both struggling. I decided to reach out again, 6 months pregnant (high risk) I ended up doing all sorts for her, and also had a toddler in tow. Anyway. As soon as my brother came back from travelling she discarded me.
Couldn't understand why I never let her meet my second born child. But I'd done everything I could for this woman who hated me.
There's a lot more history!
She shamed my mother (her own daughter) for ending her life despite my mum been utterly traumatised by her mother from her childhood.
I reached out again in covid, I got I'm OK and nothing more. Since then I've had a MH breakdown, a divorce etc and she's never picked the phone up once.
I already know that when she passes away I will not mourn her. I mourned what we could have had 16 years ago.
You need your mum out of your house, and then create boundaries with her, even if that means cutting her out completely.
She gaslights you each time she is 'nice' to you, she makes you think it's in your head. It isn't.