I spent 5-6 years dealing with something like long-covid (only it started before covid). It had symptoms that seemed clearly related to an infection, but I also noticed effects that were similar to Alzheimer/dementia. Specifically sundowning.

I would become unthinkably exhausted and my mood would change drastically between the hours of about 5:00 and 8:00pm. Later in the evening, things would magically start clear up and I'd feel closer to normal.

That was, by far, the worst period of my reasonably long life, and it's still not something I'm over, I can just manage it much better. If anyone is dealing with something similar, I'm happy to talk about things that have worked for me.