Explain the problem as you see it
I'm not sure why my Tana account has to be tied to a Google or Apple account.
Why is this a problem for you?
I like to keep everything well separated in order to be able to cut ties with a specific product at any time. I try to never use the "Login with" functionalities.
Suggest a solution
It would be much better to have a Tana account and manage the links (Google calendar only for now but many more in the future hopefully) in the app itself - would also allow to add calendars from different accounts etc.