First off, this experience is not with long-COVID but with Chronic Fatigue Syndrome. My daughter was sick for 18 years starting at age 23. Finally she went to Bastyr Naturopathic School in Seattle where she was put on an elimination diet. It didn't eliminate the CFS but she improved. She found she was allergic to gluten (i.e., no wheat, spelt, barley, rye, or oats, but quinoa and rice, ok), allergic to cow dairy (goat and sheep ok), etc. She continues some 35 years later to follow what she needs to eat and what causes problems. I learned to cook so that everything I put on the table is safe for her, for when she is visiting here. It might be worth checking with a naturopath. Anything that helps you feel better is a part of the solution to getting back to a more normal life after having long-COVID.