As the other person said it’s likely that xz is already installed on your system, but almost certainly a much older version than the compromised one. It’s likely that no action is required on your part assuming you’ve not been downloading tarballs of bleeding edge software.
As the other person said, just keep doing updates as soon Mint recommends them (since it’s based on Ubuntu LTS, it’s a lot less likely to have these bleeding edge vulnerabilities).
I genuinely don’t understand if I missed something here, and would love more explanation.