Per the article:

Scott Gessler, a former Colorado secretary of state representing Trump in the case, opposed it. He said a protective order was unnecessary because threats and intimidation already are prohibited by law.

And then they don’t explain further

I host my own, on a server in a data center on IP space owned by a friend of mine. I use mailcow for software.

Ah sorry, I missed that!

This might be more of a hack than you’re looking for, but you could probably install age in termux and put together a small shell script to operate it.

I think the reason you’re not finding what you’re looking for is because another widely agreed upon problem with pgp is that it is a generic encryption and signing tool and those turn out to be a bit of a UX nightmare. Building purpose-specific encryption into other applications tends to have much safer UX, that also tends to be less confusing.

That being said, age may do some of what you’re looking for. I don’t think it does signing but it does do encryption.

Lack of high speed rail isn’t caused by lack of knowledge about how to do it. High speed rail exists in some places, just not the US.