Family heartbreak. Any suggestions for handling the situation?

What did he expect? Sounds like it is all about him, not her.

Don't worry about it, you have enough stress already.

Not a thing. He stayed away 20 years and then was surprised she didn't recognize him. What was he expecting?

It’s upsetting to see a parent like that. I don’t know if my mom knows me but I go there because I want to see her and miss her. During Covid she was angry and would yell every time I visited her because she didn’t think I ever came to see her. But I had to rise above it and do it because I knew even if she didn’t remember i knew i came Your brother should do it for himself. As long as she isn’t agitated.

My friend, too, had to put her mom into care.

The mom had always preferred her son, but he was the first one she failed to recognize. After that it was the daughter. Toward the end, the only one the mom recognized was the daughters husband.

You can’t argue with dementia. Once it gets to this point there’s nothing really to be done.

Perhaps brother is just feeling hurt and furious of not being recognized without understanding real reason behind it?
I imagine, it will be hard to recognize people after 20 years, add dementia probably almost impossible even to remember.
Let him be and email again in few days/ weeks.
You should not be so hard on yourself, it is not your fault.

Perhaps it's best that you just let it be, as if your mother doesn't know who he is,(because it's been so long since she's seen him and because if her dementia)it won't really matter if he visits her or not anyway, as she won't remember that he was there or not. Just like she probably doesn't remember when you come to visit either, even though she may still know who you are.
Or if he changes his mind and decides he wants to visit again, tell him to just introduce himself with his name and that he's her son when he walks into her room. That might be helpful for them both.

I was estranged from my mother for over 20 years, and when she was on her death bed, I walked into the room where she lay, and she asked me who I was. I just responded with my first name, and she just said "oh." It didn't bother me that she didn't recognize me, as it had been a long time since she'd seen me.
And even though I had made peace with my extremely dysfunctional childhood, and my parents many years earlier, for my mental health, I chose to distance myself from both my parents.

So give your brother his space and let him decide what is best for himself.