I've checked firewalls, SmartCenters, and MDSs running R81.10 and R81.20 with various jumbos (up to R81.20 jumbo 53). All had XZ Utils version 5.2.2.
Only a handful of systems distributed XZ Utils 5.6.0 or 5.6.1. Most are either packaging systems mostly used by developers (such as Homebrew on macOS) or bleeding edge Linux distros (such as Debian Sid and Fedora 41 and Rawhide). This is a HUGE concern for developer workstations, and you may want to treat key material held on these workstations as compromised. Might be a problem for integration testing systems, but most aren't set up to be this aggressive about testing against new versions.
This exact backdoor is extremely unlikely to be a problem on production systems. It hasn't been in the code long enough. The way in which it was inserted, though, suggests well organized, patient attackers with plenty of resources (i.e, a state actor). As such, this exact backdoor is also extremely unlikely to be the only one they inserted.