Based on what I've read, Sxmo is not a WM, it's more like a flavored distribution/setup based on postmarketOS. It uses dwm/Wayland as WM, and many other tools to enable other features.
The SSH part claimed (based on my understanding):
1. You can read/send text messages via SSH remotely (say on your computer)
2. Read notifications too
3. Access the Bluetooth devices connected to the phone
The SSH part claimed (based on my understanding):
Kind neat.