I do know about :x to save and exit, is :X really to encrypt?

How does this work?

And how to you sync through devices and use it on e.g. a smartphone?

Or was this a joke that flew over my head?

Edit: for everybody else who didn't ever use that feature (and I've used vim as an IDE for some years), here you go
https://www.networkworld.com/article/969554/using-vim-to-quickly-encrypt-and-decrypt-files.html