Problem in sudo apt update with Proton VPN

Proton's GPG key has long-since stopped working. The simplest way to resolve this is generally to remove ProtonVPN from your source list and re-install ProtonVPN using the steps on their site.

This is how you can remove the current ProtonVPN repositories:

1. Open "Software & Updates":
2. Click the "Other Software" tab:
3. Find the items that refer to ProtonVPN and uncheck them
4. Press "Close" and, when asked if you want to reload your sources, click on "Reload":

With that out of the way, you can now run your updates without error.

If you would like to continue using ProtonVPN, then you can install it like so:

0. Uninstall the version currently on your computer using the instructions from ProtonVPN
1. Download the current-release .deb package from the ProtonVPN website
2. Using Nautilus (or another file browser), double-click the file to have it installed
3. Open Terminal
4. Update apt and install the application again:

   sudo apt update
   sudo apt install protonvpn
   

If there are still questions, the company suggests getting in touch.