I just found a doc that is giving me Pure Amino and Enteragam which is a medical food supplement. You also can find a IgG Plus brand on Amazon.
I too have had long covid since 2020, I hear it was the worst
variant. My issues are extreme fatigue and gut issues. The gut issues have lessened but still there. When I called Mayo, they said to look for an integrative medicine doctor and that is what I did. I hope it will help as all tests come out normal for all this time and it seems most don't know where to turn. Anything is worth a try. Good luck