Mom is very, very detail oriented and there is a perfect, precise process for everything. So, I am self-conscious if I have to return to the store because I forgot an item ("I always had a list I carried with me" she'll say) or if I try a shrub in the yard and the deer get it ("Oh yes, you can plant those" she'll let me know). I feel like I have lost my freedom to live an imperfect life. She is also super-thrifty and anytime I make a purchase for something for my home, she wants to know how much I have spent. I am pretty thrifty too, but she has no sense of today's prices for many things, and I know she is inwardly evaluating my every move (I hear her do this outwardly with others). So, sometimes, I don't answer these questions. I went out today, literally just to get and drive around out on my day off--yes, I know this is wasteful but my pandemic and caregiving fatigue is real (I am not yet fully vaccinated). When I came home she asked where I went. I was doing things in her suite and just absently and cheerfully answered, "out". She said, "okay Aunt Mary" (my aunt she dislikes who is socially adept at dodging things). This is the second time this week she has called me Aunt Mary. The other time was when she asked me how much I spent on my patio furniture and I honestly answered that I didn't remember. Today again, I was surprised, hurt and reminded of the lack of boundaries. I know we need a conversation. Advice, anyone?
She clearly has a very poor self-image if she has to build herself up by criticizing you.
The boundaries are for YOU to set; you can only control YOUR hehavior, not hers.
I CAN walk away. She can't.
At 91, she is not going to get 'better', so if she's making racist remarks, I simply say "Mom, that's completely innapropriate." Even if only 20% of what I say goes into her brain, I'll take that.
When she really gets going, I leave.
As we age our social filters disappear faster and faster. Sounds like your mom was probably like this in her earlier years and now it's ramping up AND your emotions are more tender due to burn-out. I'm not sure at 84 if she is capable of learning new things such as boundaries, but she might. You don't indicate she has any cognitive decline in your profile. I've been working on boundaries with my mom (who is 91 and has always been very pushy). I don't expect her to remember the boundaries or change her behavior but now I have a ready response or reaction that shows my mom the boundary at the time it needs erecting. My mom (who lives next door to us) has always made unsolicited observations about my marriage. I now respond by saying, "Said the woman who's twice divorced and been single since 1960". She keeps saying junk and so I keep having fun with it. There's nothing else to be done at your mom's advanced age except choose how you will react to it because it will keep happening. You can either abruptly redirect the conversation (as if she hadn't said what she just said) or ignore it or walk out of the room or have a snappy (but not insulting) come-back or give her an obviously fantastical story about the patio furniture costing $80,000 but you negotiated it down to $40,000. Never give her the answer. It's none of her judgmental business (because that's what she does with the info: she judges you with it so don't give her that power). She may get a little mad when you do this. She may even turn the tables on you and do it back. Just don't give her the actual ammo.
Mostly, I hope you can get a break soon -- please take care of yourself!