Update error after uninstalling Steam with apt

Question

I use Kubuntu 23.04

After unisinstalling steam with "sudo apt remove steam*" and then "sudo apt autoremove", I want to update the system with the classic "sudo apt update, sudo apt upgrade and sudo apt autoremove" but when I write "sudo apt update" I got this:

sudo apt update 

Hit:1 http://it.archive.ubuntu.com/ubuntu lunar InRelease
Hit:2 http://it.archive.ubuntu.com/ubuntu lunar-updates InRelease                                                                                    
Hit:3 http://it.archive.ubuntu.com/ubuntu lunar-backports InRelease                                                                                  
Hit:4 https://dl.google.com/linux/chrome/deb stable InRelease                                                    
Hit:5 http://security.ubuntu.com/ubuntu lunar-security InRelease                                                 
Hit:6 https://repo.steampowered.com/steam stable InRelease    
Err:6 https://repo.steampowered.com/steam stable InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
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://repo.steampowered.com/steam stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7
W: Failed to fetch https://repo.steampowered.com/steam/dists/stable/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7
W: Some index files failed to download. They have been ignored, or old ones used instead.

How can I fix it ?