The way upgrades work on the entire Debian family is essentially, update the repos to the new release and then just install all the updates. So it’s basically as if you just apt installed all packages to a newer version.
Absolute worst case it would uninstall PipeWire and reinstall PulseAudio, but more likely it would refuse to proceed due to unsolvable dependencies. If the new Mint switched to PipeWire by default, it won’t do anything more than possibly updating PipeWire if there’s a newer version.
Upgrades really aren’t that special, it’s just installing newer versions of packages, updating configs and bringing new recommended packages, removing ones that are no longer needed.