You can run commands, so systemctl poweroff should work to turn off your computer (on Linux, not sure how KDE Connect works on Windows, but I’d assume there’s an equivalent)

A quick search led me to Passbolt which has multiple user support, native installs for both Debian and Fedora (you’ll need to add their repo manually, though) and an Android app, so it seems to fit all your criteria.

Just curious, are there any specific reasons you wish to avoid docker?

It seems to me like you’ve kinda made up your mind and are just waiting for someone to back you up before dropping the cash for the Vero :P

With the criteria you’ve listed, I doubt you’ll find a better solution. I say go for it (as long as you can afford it)!

Did you bother opening the link? This project is clearly much more elaborate than simply synchronising notes.

Don’t quote me on this, but I think you’d have to add --volumes