Sounds like my life recently. Condolences for your grandmother.
The long term effects of COVID are pretty scary from a medical pov. We just don't know enough at this point, but I think that it may end up worse than the initial infection or even dying from it. I read somewhere a while back that COVID is creating a whole generation of people with long term disabilities who will require increasing resources as time goes on. The drag on society as a whole could completely alter the way we live.
I had brain fog for years after 2 bouts of cancer treatment 9 years ago. It still comes and goes. My memory is pretty good, but I still struggle with concentration at times. I tried a few treatments back then, but they were worse than the fog (kept me from sleeping for several days at a time). Hopefully your own issues will resolve to some sort of normalcy in the near future. If you don't already, I would recommend trying some meditation. It's the only thing that helped me. 20 minutes 3-4x per week. Intense exercise can also be beneficial, but as I get older that becomes more difficult.