I saw the chart in this article a while back and it might help. I haven't had Covid, but I did have a pretty bad post viral reactivation a few years ago and found a fitness watch really helped me monitor activity - especially resting heart rate, HRV, and what they call Body Battery. I think the go to advice is to ramp up way slower than you'd like. Long Covid really seems to be hitting athletic people.
https://health.clevelandclinic.org/returning-to-sports-or-exercise-after-recovering-from-covid-19