Adam

Then messages sent outside ProtonMail are not PGP-signed (while Android app is able to do it)

Seems like both PGP signed and PGP encrypted emails are [supported](https://protonmail.com/blog/protonmail-v3-14-release-notes/)

That's what I was afraid of. Would instructions to train a dataset on one's own be more in the clear? I have no idea about hardware requirements, though.

I don't have the hardware either. And I guess if detailed instructions were published, that could still get DMCA'd as did tools like yt-dl