Welcome to this group Totto. Sorry to hear about your struggles. In one of my previous posts I mentioned that our limitations are difficult because often we don't know where the line is until we have crossed it. Then we pay the consequences.
With your family gatherings, it is difficult to say no, but sometimes we have to. A simple "right now my brain can't take it" should work with understanding, caring people. COVID also gives you a good excuse. If you do go to a gathering, can you do what my wife does, off to the side with just 1 or 2 others, away from all the noise. Hard to do for an extrovert, but you have to think of your whole self. Also, there are no rules about how long we have to stay. Very hard for Minnesotans, but going for part of the time will let them know you enjoy being part of the family, but leaving early will help them to know your limitations. I'm finding out that these limitations are not short term. It's been 2 years now for me and my energy level and stamina are not what they used to be. You are much younger, but that is all the more reason to listen to your body and get your needed rest. Over doing it really hinders the healing process.