This is the reason why I've not used them, it's an instant turn-off needing to use Google SSO

Yes I looked at that one also but it was an insta-dealbreaker for the same reason. There's many options around, luckily. So no need to go for something as compromised as this.

Another dealbreaker for me is hosted configuration and access management. I want to be the only one managing it.

They support GSuite and azure AD it appears. So it is not limited to just gmail. When you pay for GSuite I think it will be a bit less risky than when using their free gmail offering.

Regardless, it would have been nice if you could use your own identity provider.

They are: https://github.com/tailscale/tailscale

A fair bit of the client code is also on the repo. Things like role based access control that require a backing store on tailscale side aren't open.

the client is here https://github.com/tailscale/tailscale