Open .gpg files with text editor

I’d like to open .gpg files into the builtin text editor, so that later I can decode them with some browser extension and my private GPG key.
From what I got I need to create a custom mime type mapping, as already covered here, but it’s not working for me.

I created config/mimetypemapping.json with:
“application/pgp-encrypted”: “text”,
“gpg”: “text”

and ran occ maintenance:mimetype:update-js but the gpg files are still being downloaded. I found another thread but sadly it has no solution posted.

Any hint on how to open GPG files inline?

It would be great to have a native GnuPG Nextcloud app integrating opengpg.js, but it’s currently beyond my capabilities right now…