If you're up to trying some supplementation, after my Delta infection in October I took a PQQ-CoQ10-glutathione-NAC combo that my local store recommended, along with some straight NAC, and my lingering fatigue cleared up about a week after the illness had abated. There are lots of other long COVID recovery protocols out there which are pretty easy to find -- who knows how much of it is snake oil, but as long as what is recommended is safe, possibly taking some placebos is a minor risk to run for a chance at some relief IMO.