There's some research going with on long COVID which is looking at the possibility that some people are developing micro clots, which then limits the amount of o2 getting to your organs, including your heart. The standard tests to see if people have more normal clots won't pick these up, tis just a possibility though, but could be why you're getting this ?
I think, but aren't totally sure, that there's a trial going on with new, and repurposed drugs ( Aspirin I think ) ? Best not to self medicate with Aspirin though, it can cause stomach bleeds in some people.
The standard advice for anyone suffering a bit post infection is to take it easy and reintroduce things gradually, which must be very frustrating if you're normally active, but is good advice. Chances are, if it's COVID related, it'll sort itself out eventually, but getting it properly checked out makes sense too.
edit : All runners that post on running forums are nutcases, taking advice from them on health matters should come with a formal Health Warning !