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.

Start small in anything you pursue and gradually improve each day. If running, start with walking. If weight lifting, start with the bar. Do something that grounds you and challenges you at the same time so you stick with it.