On the Linux Mint Software Manager the Xz-utils says Version 5.2.5-2ubuntu1. But the Backdoor exploit was affecting Xz-utils versions 5.6.0 and 5.6.1. So check your version. For me - before confirming versions I uninstalled the version that was installed on my machine quickly just to be safe. But it must've been version 5.2.5-2ubuntu1 on my machine which supposedly is safe.
Flagging this, this was the package which had a potential backdoor in it... not sure how one can detect these on this or other packages though.