A study to prove/disprove long term COVID issues seems awfully difficult or impossible, especially for minor, objective things (fatigue, taste, “brain fog”, etc

A study to prove/disprove long term COVID issues seems awfully difficult or impossible, especially for minor, objective things (fatigue, taste, “brain fog”, etc). Are we relying on patients to self-report whether they had COVID, what they long term effects they noticed? If so, it seems like we’re testing mass hysteria as much as actual effects. I was likely infected and noticed the taste/smell issue. Since I’ve recovered, so has my taste/smell but it was not an immediate recovery and I have no idea if I “lost” some amount of scent sensitivity. It is probably the same as pre-COVID, but if I heard others were reporting this issue it would be very easy to convince myself that I did lose sensitivity and report that.