This is what I see on shell:
purism@pureos:~$ sudo apt update
[sudo] password for purism:
Hit:1 https://repo.pureos.net/pureos byzantium InRelease
Hit:2 https://repo.pureos.net/pureos byzantium-updates InRelease
Hit:3 https://repo.pureos.net/pureos byzantium-security InRelease
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
and the screenshot shows what the app PureOS Store
thinks. Why it even wants to downgrade versions?