I too have a difficult relationship with my mother. Having my own children really brought my emotions to the forefront and I had to reconcile those feelings / the contrast in how I mother my own children. My feelings about her have recently become much more settled and I see the positives, and I love her, but it will always be sad.
I find it really unhelpful when other people who don't know my mother at all come and minimise my experiences, presumably out of some defensiveness they feel (projecting themselves into my mother's role?), so I just wanted to say what you are going through is not trivial. You don't need to "be wary of armchair diagnosis" you are trying to understand and process what you KNOW about your mother and these labels are just for you.
I have come to frame many of my mother's shortcomings in the context of her own abusive childhood, probable/possible neurodiversity (more broadly, her limitations) and her constant need to soothe herself - probably because of the first two factors.
Children need to have a mother to soothe them - from an evolutionary perspective it's not just a nice-to-have but a matter of life and death. If you don't endear yourself sufficiently to a primary carer (a mother) to evoke adequate caregiving responses, you die. Sadly this is still the fate of many children. This deep, pervasive biological urge to be loved by a mother, our first longing and first instinct stays with us for life I believe. It's the reason why as an adult woman and a mother yourself, your relationship to your own mother still feels so relevant. It may also be the reason behind many of her behaviours.
Eg one facet of your mother seems to be a need for validation/attention which has paramount importance to her and she lacks both the insight and the emotional/social tools to deal with that and function well as a mother/grandmother at the same time. If that relates to a deeper emotional need to be loved / seen / soothed as a child then it probably emotionally feels like survival to her, and being without validation/attention may emotionally feel like a survival threat. In another life she could have used some talent of hers to be highly successful, not become a parent at all, and her needs might have been better met and her shortcomings could have gone by the by. Equally, perhaps not depending on how dysfunctional she is.
Unlike your mother who is emotionally distant, mine was enmeshed and parentified me. She used me to soothe herself. It's all shades of the same thing - emotional immaturity, overwhelming needs of their own etc. I found the book "Understanding the Borderline Mother" helpful for understanding how my mother could feel like very different people at times (though I think "Borderline" is probably a defunct label) and also just validating how horrible (and also confusing) that was for me at times. It might not be such a good fit for you but you could try it. I found the whole thing online as a free PDF. It made me feel like I could make better sense of it all, and that I wasn't just mad / imagining it.
I think probably both of our mothers don't/didn't know how to be different. They also existed within a different parenting culture where I think emotionally supporting your children wasn't the focus. Emotional awareness in general, was on a pretty low ebb I'd say for those raising kids in the 80s/90s. Many people from that generation drink a lot, for a reason I think! There is a legacy of multi generational trauma perhaps from the first and second world wars, and/or from the extremely weird quasi-industrial parenting practices that were popular in the 50s and 60s.
The internet, with all its access to information, support and solidarity didn't exist either for our mothers. So it was more difficult for them to understand and process their own emotional issues. I think a lot of people (not all) really fix in their ways from middle age onwards, and very possibly much earlier than that.
Anyway, the point of this was really meant to be solidarity. And to say, yes of course it really matters. Even though it was in the past. Even though she won't change. I think you will feel many different things at different stages as you process your relationship with her, perhaps including hatred, anger and resentment. As your mother is dying, you might still be going through those feelings after her death. I'm sorry for the extra difficulty that may cause you. My advice would be to accept those feelings forgive, don't feel guilty or shame yourself for them, but also don't act upon them hastily. You seem like a thoughtful and conscientious person. I think you'll gain wisdom from your pain, unlike your mother.