Viruses require a host to replicate. There would have to be life on Mars in order for viruses to persist there. I’d be more worried about some type of soil bacteria that can live in extreme conditions - and or bacterial spores.
Whatever. We have enough to worry about on this planet.
We might be immune to anything coming back from there, because it doesn’t know how to attack our system.
The same way we don’t get dutch elm disease, or trees don’t catch a cold.
Roll out the US Space Force exo-biologists !
( President Trump was prescient.)
https://www.youtube.com/watch?v=3Pns-2wfuu8
“Might”, “possibly”, and “could” are not words of science.
More likely that the astronauts would bring Earth viruses to Mars.
Jeez, just where do they thing COVID came from? (just kidding, but people act like it)