No GPG key entry?
In previous versions of Seahorse at the left I could select "gpg keys". This is not possible anymore, as it seems, or it is broken.
I also cannot create a new PGP key from the "New" menu:
However, I can import keys in the "import…" menu, which is really strange. They just appear nowhere in the GUI.
seahorse 3.20.0 Fedora 28