I had a hard time too when I first tried to get netbird going but reading the https://docs.netbird.io/manage/access-control section of the docs cleared things up, especially the part about not putting all your devices in the same group.

For those of you who are interested in this but don’t know where to start I think https://www.freedombox.org/ may be a good starting point. It’s been around for a long time, provides easy enough installation and a nice web interface for management. Its based on Debian and you can give it a try on their demo.

Also the vision for the project aligns pretty much with what op is saying https://wiki.debian.org/FreedomBox/Vision