While investigating another issue [1] I came across this Debian installation report which mentions the version of nix. Specifically that only nix version 2.18+ is supported.
But on my flox/nix setup, installed via the Flox deb, I have:
$ flox --version
1.3.1
$ nix --version
nix (Nix) 2.17.1
I have not installed nix from the Ubuntu 22.04 repos (that one is 2.6.0).
So, as far as I can tell, the Flox team is providing an unsupported version of nix in their deb?
[1]: A nix syntax error when I try to install nixGL