I'm 69 and got covid in March on a 7-day 350 mi bike tour. I got a double cytokine storm from getting glutened (celiac) and covid exposure the same day (a cyclist had covid and shared it with us). I averaged ~6000 mi/year on my bikes. My long covid (LC) is gradually decreasing (ups and downs) and I manage it by short rides (5 to 10 mi max) with rests between, taking walks, lifting weights (non aerobic doesn't seem to hit LC), managing stress and getting enough sleep are critical, and slowly ramping up mental and physical activity on the good days. My hypothyroidism also worsened; getting a synthroid increase helped a bit. Once the LC goes away (optimism) ramping up my exercise will be hard, but so is any training. It almost sounds like your immune system was torqued and can't quite rid you of the covid nasty bits. You might consider a log of your meals, in case any food groups worsen your symptoms. My celiac was triggered 14 years ago after catching H1N1 so for me it is gluten and NSAIDs. It is tough going from century to decade rides.