Have you considered that when you feel better you’re more likely to try hiking/travel to places with higher elevations? And you could be mixing up correlation and causation?
Or that many people with long COVID feel better in the short term (days weeks or months) after exercise due to adrenaline, but it sometimes leads to a long term worsening through PEM. As someone connected to a couple researchers and serving as advisor to a government research effort, I’m not sure I see anything worth spending the very limited resources researchers have here.
You might want to clarify what long covid subtype you have though so I can make a mental note incase I hear something similar from someone else with a similar subtype.