I found this Vox podcast really enlightening about “long COVID.”
It talks about how all serious pathogens can, and pretty much do, give rise to similar long-term symptoms. So, one thing about long COVID is that because so many people are sick at the same time, there are many cases of this at the same time. So, it can be studied, and people are being believed rather than brushed off more. But Covid isn’t unique in causing these kinds of medically unexplained sequelae.