root@ubuntu:~# apt update
Err:4 Index of linux/ubuntu/ focal Release
Certificate verification failed: The certificate is NOT trusted. The certificate issuer is unknown. Could not handshake: Error in the certificate verification. [IP: 18.104.22.168 443]
It is likely to be related to your other certificate issue
The reason could be your local network security settings.
Note: “Docker Desktop for Linux” category is for “Docker Desktop for Linux”, not any Docker version that runs on Linux. If your issues are not related to Docker Desktop, DockerEngine is the right repository. Since you haven’t mentioned Docker Desktop in the other topic and the issue itself is not related to it, I moved it to DockerEngine. Are you trying to install Docker Desktop?