Turris Omnia Attempts TurrisOS 6 but Update Fails

I think updater is trying to upgrade your Omnia to TOS 6.0.
You can find the following in the 6.0 release notes.

:package: Other Changes

  • Obsolete SIDN package feed dropped

I have removed the package feed SIDN and the wireguard package and installed the package kmod-wireguard instead.
Now the update to 6.0 is working.