

It’s using plasma-nano session, which is a minimal Plasma session, and adding a launcher and settings app from what I can see.
You can run it in a regular window if you install the dependencies and use kde-builder to compile it and run. See the Dev docs at https://invent.kde.org/plasma/plasma-bigscreen/
If you do decide to install all the kde-builder stuff, I’d suggest you use a distrobox container to make it easy to remove the many, many packages that it will install in order to set up the build environment
Use tailscale and keep your services behind the VPN. Opening up your services, even behind a tunnel, isn’t a thing you should get into early in your self-hosting journey.