Fixed the problem myself. For future refence, osdetect checks /etc/lsb-release and in my case that file had not been updated correctly.
So after I fixed the version information inside /etc/lsb-release everything works.
Thanks Peter but refreshing the components didn't fix the problem.
From poking around the plesk tools it seems that "osdetect" is the source of the wrong version information.
# /opt/psa/admin/bin/osdetect...
It looks like sury doesn't host packages for stretch (Debian 9) anymore (Debian 9 LTS support has ended June 30 2022)
More information
https://github.com/oerdnj/deb.sury.org/issues/1785
I have a problem with the Plesk updater insisting I have Debian 8
There are no products for your operating system
( 'Debian' 'Linux' '8' 'x86_64' ) available
from the selected source.
My dist-upgrade completed without any problems, everything is working great on the OS side.
/etc/os-release...