Ubuntu 20.04.6 LTS apt problems - how to upgrade f/w?

[Bo Berglund]

I am running an Ubuntu 20.04.6 LTS server which is headless and only accessed
via putty SSH.
Today I was going to update the system and received this message on the login:

*** Kernel upgrade required. Kernel 5.4.0-89.100-generic Livepatch coverage has
ended ***


I assume that means I have to run an apt full-upgrade on the system so I started
by:

sudo apt update

This generated another error:

Err:7 https://apt.svtplay-dl.se svtplay-dl InRelease
  The following signatures couldn't be verified because the public key is not
available: NO_PUBKEY D3D19C99F5FA3AA7

and at the end:

All packages are up to date.
W: An error occurred during the signature verification. The repository is not
updated and the previous index files will be used. G
PG error: https://apt.svtplay-dl.se svtplay-dl InRelease: The following
signatures couldn't be verified because the public key is
not available: NO_PUBKEY D3D19C99F5FA3AA7
W: Failed to fetch https://apt.svtplay-dl.se/dists/svtplay-dl/InRelease  The
following signatures couldn't be verified because the
public key is not available: NO_PUBKEY D3D19C99F5FA3AA7
W: Some index files failed to download. They have been ignored, or old ones used
instead.

Since I no longer use svtplay/dl I uninstelled it:

sudo apt remove svtplay-dl

Err:4 https://apt.svtplay-dl.se svtplay-dl InRelease
  The following signatures couldn't be verified because the public key is not
available: NO_PUBKEY D3D19C99F5FA3AA7

but later:

All packages are up to date.
W: An error occurred during the signature verification. The repository is not
updated and the previous index files will be used. GPG error:
https://apt.svtplay-dl.se svtplay-dl InRelease: The following signatures
couldn't be verified because the public key is not available: NO_PUBKEY
D3D19C99F5FA3AA7
W: Failed to fetch https://apt.svtplay-dl.se/dists/svtplay-dl/InRelease  The
following signatures couldn't be verified because the public key is not
available: NO_PUBKEY D3D19C99F5FA3AA7
W: Some index files failed to download. They have been ignored, or old ones used
instead.

I don't get this, svtplay-dl IS uninstalled so why is it still generating
errors?

apt policy svtplay-dl
svtplay-dl:
  Installed: (none)

What do I do now in order to make a f/w upgrade as was the original task?


-- 
Bo Berglund
Developer in Sweden