Yes I have those similar symptoms in my legs and arms with extreme weakness during activities/exercise. If I workout I have lost all my strength and endurance, and afterwards I’ll be in unreasonable pain for a longer than normal time.

If you look up long covid PEM it may help describe your symptoms along with explaining the research as to what’s happening on a cellular level and why none of the tests can diagnose it. I’ve also had the nerve function tests, MRI, CT, autoimmune test, every blood screening imaginable with very little to diagnose or treat.

I was also just diagnosed with fibromyalgia, which again if you look it up there is also data about long covid/fibromyalgia diagnosis's after covid infection.

I never knew anything about fibromyalgia but some of my symptoms match that too and some symptoms I was having but thought it was “age related”…..

Hope this helps to give you answers but it doesn’t help for any resolution from my experience