Well, first off "normal" antibiotics don't kill viruses so that kinda makes it different from the start. But even then, most antibiotics kill bacteria etc through disrupting their cellular processes and leaves the DNA mostly alone. Resistance against antibiotics is created through natural evolution; those bacteria that can survive better in an environment where antibiotics will reproduce more than their cousins which can't.

OTOH, Molnupiravir works by: (quoting from Wikipedia again)

> [it] exerts its antiviral action through introduction of copying errors during viral RNA replication.

So it deliberately stops virus reproduction by introducing errors in RNA copying. The vast majority of time this just makes the virus nonfunctional, but it is technically not impossible that it creates a viable mutated strain. This mutated strain may or may not be worse than the original virus. It is not unsimilar to how `cat /dev/urandom | bash` just MIGHT start off with `rm -rf /` and delete everything, but usually it will just create a crash because the random bytes don't parse into a valid bash command.