Issue
I'm was trying to add Ubuntu repository on Debian, but get an error:
Err:11 https://mirrors.ustc.edu.cn/ubuntu focal InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4FE6ACC0B21F32 NO_PUBKEY 871920D1991BC93C
How to fix it?
Solution
theoretically you can import the missing GPG key to Debian but it is a bad idea.
to import the missing keys to Debian you must go:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 871920D1991BC93C
normally you should check out there always is the same package also in a Debian repository. Best solution is to add the right Debian repositories.
Answered By - Max Muster