Even if your cat is infected with FIP, the neutering is safe to do,I. I have gottenhad this done to a feral cat iI had a couple of years ago (actually it was done at the same time as a tooth was extracted as a result of FIP).
I can notcannot answer how safe it is to spay a female cat that has FIP, but iI do not think the risk is significanlysignificantly elevated in female cats.
Cats can get a number of corona virusescoronaviruses, but covid 19COVID-19 is not one of the ones that can infect cats or dogs.
This question is related to the corona part of your question: Cat health consideration regarding the coronavirus
Neutering a cat is a simple and easy operation that causes very little stress for the cat and your cat will not need any special care after this have been done.