Bttrfly - tell your brother from another to try a low histamine diet and two kinds of antihistamines - a non-sedating antihistamine like Zyrtec or Claritin (called H1 blockers) and the stomach acid blocker Pepcid (a different kind of antihistamine called an H2 blocker). I follow an online group of Long Covid patients, and of all the things they have tried, this seems to be the intervention that helps the most people.
Also many long haulers seem to develop POTS, when they do they may respond to POTS treatments like beta blockers.
