The public keys can be stored anywhere, it doesn’t matter. That’s why they’re called public: because they’re not private, they’re not sensitive, they’re not a secret.

They could be, but 2M new Brazilian users after Twitter’s block there actually seems quite low and definitely credible.

That makes zero sense. Where did you get that idea from?

For reference, here are their docs describing key management. https://tailscale.com/blog/tailscale-key-management

I found Tailscale to be easier to install and configure than ZeroTier, and also to have better performance.

I have never used Twingate.