I have also tried to update my running 4.2.8 installation without success.
I used the new installation instructions regarding the cloudsmith repositories, but it does not work.
Searching manually through
https://cloudsmith.io/~tvheadend/repos/tvheadend/packages/ I found the reason.
In cloudsmith repository are "thousands" of different versions for a lot of distributions including Ubuntu 22.04 Jammy, but NOT for amd64. This particular version is missing.
Is there a technical reason why the jammy-amd64 package does not exist in cloudsmith?