From my experience in caring for my elderly parents for several years before they died in their 80s, I would say that your mother is actually doing better than many people of her age, and perhaps you would be better off accepting the changes that have come with her advanced age, rather than bemoaning the fact that she has "given up". Just because she doesn't cook from scratch doesn't mean she's given up - on the contrary, she seems content to microwave ready meals and is presumably eating them, which is a good sign. The fact that she is seeking medical help for her various ailments (imagined or real), is also a good thing - my mother avoided doctors at all costs and ignored various issues until it was too late to do anything about them. Also, elderly people who live alone do have a tendency to dwell on every small symptom and imagine the worst - maybe she just wants reassurance.
When my mother was 84 she was barely eating, due to various digestive problems that were too late to fix. She lived mostly on soup, hot drinks, custard and sweets, for years. Left to her own devices she barely washed or changed her clothes, so had to be coaxed by me to do these things. As time went on she couldn't be bothered to go to bed, stayed in her chair day and night, and in the end she stopped using the toilet so had to wear incontinence pants (which she never changed, without prompting from me/the carers). Although her legs worked fine, through lack of use the muscles gave way and she could barely walk to the toilet, even with help. I could write several pages about what giving up real looks like, but hopefully you get the picture.
Being old and alone sucks. It's a shame when elderly people don't try to keep active, or attend clubs and activities that could benefit them, but if they don't want to do it, you can't make them. I understand why you feel frustrated as you think life would be so much better if she made more of an effort to help herself, but this depression and apathy is very common in her age group so try to accept that she's unlikely to change now. I know it's hard becoming the main carer to parents that have been less than caring towards you (mine weren't perfect either), but you will find time with her easier if you just go with the flow a bit and just gently help her with anything you can, to keep her ticking over. It may take years for your mother to fade from existence, or she may be gone tomorrow - you just don't know. But when she's gone, you will feel better if you know you did everything you ressonably could to support her through her final phase of life. That doesn't mean sacrificing your own health - you need to set your own boundaries about how mucn you are willing/able to do, to help her through her twilight years. It's hard. Good luck OP.