One of my frustrations with covid and the vaccine is that we're two and half years into this pandemic and we have no data for runners. We're arguably the world's largest running forum. We should have surveys and data to show that X% of covids are okay in Y days, Z% has lingering symptoms, and so on so we as runners would have a better idea of what to do and what approach post-covid works best. Instead, every covid/vaccine thread gets hijacked by trolls.
Back to the OP's question.
If you've taken Paxlovid, there is sometimes a rebound covid about a week after finally testing negative.
Mild initial symptoms don't mean there will be no longer term symptoms. Lingering fatigue is a... well, I can't say common symptom because we don't know, but many mild cases report lingering fatigue.
Personally, I'd skip the marathon and pick a fall marathon. July isn't a great time to run a marathon anyway. Blood clots are a long covid problem and they can kill you... it's not like a sore knee you just rehab for a few months.
If you do run, pre-decide before starting that if you don't hit your goal splits or you're struggling with what should be an easy early pace that you will drop out. If you don't pre-decide to DNF then your brain might default to the "finish no matter what" mentality.