> it's unclear what long covid is

It's just another post-acute infection syndrome that can occur from pretty much any contagious illness (flu, etc.). Most people reading this have probably experienced this. Ever had a cough that persisted multiple weeks after the rest of your illness went away? That's not because your cold permanently damaged your lungs or even that the virus is still around. It's because your immune system will sometimes get confused and continue to wage war in your throat (or whatever it thought was infected) long after the virus has been eliminated.