The problem is that the package maintainers are trying to follow Chromium as closely as possible and therefore support for older version of Ubuntu is dropped rather soon.
All releases shall be supported on a best-effort basis.
x86_64is the only architecture we can be reliably test so any other architectures will only be guaranteed to be buildable at best. Older releases may be dropped at any time if they are too difficult to continue to support due to how bleeding edge Chromium tends to be.source: ungoogled-chromium-debian
You could try to download and install the binary release, the only downside is that it won't update automatically, in which case you may be interested in an updater script.
Or go for the flatpak package.
Otherwise, just wait for ZorinOS 17 and then add the Jammy repositories and install from there.
Ungoogled Chromium is not Chromium.
Chromium is the open source browser used as the base by other browsers, including Microsoft Edge or Google Chrome itself. Ungoogled Chromium removes all dependencies to Google web services.
As far as I can tell, it's not in the default repositories.