Their Team and higher plans integrate with Okta, their Business and higher sync group memberships and deactivated users with Okta, and their "contact us" Enterprise plan supports custom SAML and OIDC. I think this is a fair tradeoff of cost vs benefit given who needs each solution and how much individualized time and energy Tailscale needs to spend per customer to support each of these solutions.

Yeah that makes a lot of sense. Given how the protocol is used in practice it does require a lot of support. I understood the parent comment as them only supporting Google.

They don't support TailScale-specific email and password accounts in any version, and only Google or GitHub login (or maybe MS accounts?) in the free version. That was the basis of the complaint, I think. TailScale has written separately about why they made that choice.