Cant update Ubuntu, neither using the terminal nor using the setting

Question

I'm a total newbie to Linux as in Ubuntu, recently thought of switching over to Brave browser and thought of deleting MS Edge, since then I cant update (LTS 20.4) instead of update, I get the revert option onlyenter image description here

Answer 1

The error actually tells you what is wrong:

The repository https://packages.microsoft.com... is not signed. The public key is not available.

When you installed Microsoft Edge, for some reason the public key was not added properly.

To get rid of this error you need to review the original steps you followed when you added the Microsoft Edge repos and see if you can get the public key added correctly.

Or, you can use a text editor to edit your /etc/apt/sources.list. Delete the offending line or comment it out by putting # in front of it.

Alternatively, there is a usually a GUI way to remove sources. Using the KDE desktop environment, the options are in Discover. In GNOME you can change sources in the Software Center.