I gave up and just setup wireguard directly instead, I don't trust Tailscale either if that's their attitude towards privacy, it's permanently marred my vision of their product.
There also exists an open source implementation of the tailscale control server [1] that you could self host.
People sometimes ask me to describe the differences between Nebula and Tailscale. One of the most important relates to performance and scale. Nebula can handle the amount of internal network traffic and scalability of nodes (100k+ nodes, constant churn) required on a large network like Slack's, but Tailscale cannot. Tailscale's performance is fine for many situations, but not suitable for infrastructure. It is just a fundamentally different set of goals.
Nebula was created and open sourced before Tailscale was offering their product, but their architecture is similar to older offerings in the market, and is something we purposely avoided when creating Nebula.
Fwiw, I even recommend Tailscale to friends who want to do things like connect to their Plex server or Synology or [other thing] at home remotely. It simplifies this kind of thing greatly and doesn't require you to set up any infrastructure you control directly, which can be a headache for folks who just want to reach a handful of computers/devices.
That having been said, I also am wary of using Tailscale for the same reasons as above, I have to trust Tailscale and Github? I can maybe justify trusting Tailscale, but trusting GH/Microsoft/other SSO provider is a bridge too far.