After further research, I was under the wrong understanding. You are correct that Mullvad still receives your public IP even if routed through Tailscale.

Obviously seems to be an industry-wide problem, but I hope both you and Tailscale can consider alternative endpoints for those who don't want to rely on the Mullvad infrastructure.

Diversification of endpoint providers will help insolate your company from a collapse if Mullvad decides to sell out, and make you more attractive to former Mullvad customers turned off by their Co-Founder's investment of their privacy dollars into extreme right-wing politics.

As far as I know, they don't plan to part ways with the "great replacement theory" executive staff being paid enough to be the highest contributor to the Swedish far-right party Örebropartiet. You have to question whether their highest-paid staff's loyalty to far-right politics influences Mullvad decisions and future partnerships.

Cross the Örebropartiet, and you might be issuing refunds a year from now.