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.
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.