PSTN, I don’t know of any way to encrypt the call

Many calls are VoIP nowadays though, which could be encrypted depending on your provider and upstream SIP trunks. It’s probably not end to end though, so your carrier can still spy on you.

They probably run it more than once a week :)

This is not to counter your point (I agree they should probably offer a client to sync files on Linux), but rclone recently added (beta) support for proton drive, so you might want to check that out if you’re still using it.

I’m not sure about pulseaudio but snapcast is time synced.