Its funny, my dad and I never bonded, I was the third born and somehow I didn't seem to register on his radar, only at the end of his life, in a way I can understand the overcompensation, something I did all of my life with my dad, to no avail for the most part -whatever I did it was never good enough. My mum was a different soul completely. I don't bother thinking about that now too much, because in the end he had no one else really to trust, he'd fell out with my sister and taken sides with my eldest brother, which created animosity between him and my mum, which left me as the go between (piggy in the middle). I did what I could do for him in what was a very short space of time, even though our past was a rocky one, he was my dad despite our differences. Dad died from an aggressive cancer, it was everywhere, but because he had cancer he got everything done from EOL to hospice care -nothing was an issue. My mums story with dementia is an entirely different one, eveything about it has been arduous, but at least unlike your experience mum is on a palliative pathway and I don't have the worries you have.
You are strong DoD, so please don't loose hope and keep fighting xx