I’m not a Covid denier or anything either. I masked up and stayed in during the pandemic, I got the vaccine, etc. I had original first year Covid confirmed by a test, and I’m positive I’ve had it at least once again since then though didn’t get a test confirmation, so I’m 100% positive Covid is real (I feel like this is an obvious statement but I’m sure some people out there believe it’s a hoax or something). However I’ve seen exactly zero evidence other than online anecdotes that Long Covid exists or ever existed.
If it’s “vastly under diagnosed” I should personally know multiple people with it and should likely have family members with it (at least extended family) and yet I don’t. Not a single person. Honestly I think it’s one of those terminally online things that gets repeated a lot but only online.