How do you reliably measure actual weakness of muscles? There is a huge neurological and psychological component to strength. My level of motivation and willingness to suffer has a huge impact on the amount of force that I can exert in a strength test. If I think I'm sick then that reduces my confidence and my ability to perform to my maximum potential even if there's nothing physically wrong.

That said, I do think there is probably some mitochondrial dysfunction going on in a subset of Long Covid patients that reduces muscle strength. But we don't have a good way to measure it and don't even know what to look for.

I'm not sure how that's unreasonable. Depressed people tend to lounge or lay around in bed all day, tired, sad, feeling helpless. I can days or weeks causing muscle atrophy (maybe not a ton) but enough that when actually move you feel sore. Perhaps they've stopped going to the gym. Some people tend to under eat while depressed which can lead to no energy and your muscles not getting adequate nutrients which could cause cramps and pain.

So it's seems absolutely possible to experience "actual weakness of muscles"

Yes.

Absolutely.