My understanding is that even once symptoms have cleared , even if your symptoms were mild, you will still have some damage and inflammation in your major organs. It may just be heart and lungs , it may be more widespread such as kidneys. Just because the symptoms have gone doesn’t mean any damage caused by the immune system battle is repaired in same timescales.
I would take any initial time back on the bike easy. Do a 1 or 2 hour session below your LT1 and compare your heart rate, power and perceived exertion. How do they compare to normal, how much are they out of whack?
Next time out push it a bit harder and again pay attention to heart rate, power and perceived exertion. Do they feel aligned like usual or out of whack? If say you push as hard as 80% max HR does your breathing match up, does it feel like you could go harder, or does it feel like you are maxing out on perceived exertion?
If it doesn’t feel quite right then back off and drop the intensity. If it feels ok push a bit harder next time.
I haven’t had Covid but I had a heavy 10 day cold beginning of October. A week after symptoms cleared my perceived exertion was well out of whack with my HR. I’d be at 77% of my max and feel like I was at 92% of max HR. Like I didn’t have much extra in the tank. It just didn’t feel right. It took me about 4 weeks after end of symptoms before things felt right and I could push up into that 90-100% of max HR band and stay there a while.
Good luck with recovery