Just as a side take (since you seem to be a Tailscale user): have you ever tried the Handscale OSS version of Tailscale?
Discussion
I actually found out about it when looking into whether Tailscale could be added to zap.store; haven't tried it yet. Do you know if you can use it with an existing Tailscale account?
It replaces tailscale.com as a coordinator, so it has it's own "account" management and domain name for the tailnets, etc.
If it were packaged for Start9 or Umbrel, that would be fantastic.