OS version is 5.1.7 Hera. I got the following error when I try to update in app center:
- W: GPG error: http://repo.vivaldi.com/stable/deb stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 793FEB8BB69735B2 - E: The repository 'http://repo.vivaldi.com/stable/deb stable Release' is not signed. - N: Updating from such a repository can't be done securely, and is therefore disabled by default. - N: See apt-secure(8) manpage for repository creation and user configuration details.
Since the problem seem to be vivaldi, I tried to remove it (I don't use it anyway) using
sudo apt purge vivaldi,
sudo apt-get purge-vivaldi-stable, and
dpkg -l | grep vivaldi. After that I tried to update again, but the error persist.
I also tried to try to import all missing GPG keys using
y-ppa-manager, but the error still persist.
I don't understand how to fix it, so any help will be appreciated. Sorry for the trouble and thank you.