Kleopatra is a certificate manager and GUI for GnuPG. The software stores your OpenPGP certificates and keys. It is available for Windows and Linux
Most of the GUI tools for openPGP under Privacy Guides are for Windows and MacOS so I suggest this as an alternative GUI for Linux.
This front end is included with the gpg4win package on windows, that we already recommend.
On Linux you may not necessarily want to install it, for example if you’re using GNOME, you’ll probably want to stick with Seahorse.
Probably not too much need to add every user interface for PGP, (there’s a lot of them).