Trying to deduce illnesses we have that would have normally occured if we never had Covid is what I try to think of rather than hanging my hat on Long Covid for the answer every time. Is it possible that your circlitory system is effecting your problem not enough oxygen in your blood flow for your muscles to respond properly. You might want to consider getting a Brackel Test on your legs for P.A.D.
Just a thought! Not a Physician just an old man that's been through Severe case of Covid an natural illnesses and getting stronger everyday by looking at both sides of the coin. Best of luck on you overcoming your obstacles!