Migration from Kinde

Another doubt is if at some point they will allow the email + OTP to use our own interfaces and pass it through some endpoint or prop the OTP that the user puts to see if it is correct, allowing large companies to create our own interfaces since their editor is not the most customizable.

You are certainly not tied to using Kinde, you can export your data at any point - https://docs.kinde.com/manage-your-account/your-data/exporting-data/?r=search#_top including hashed passwords. Does this answer your question?

Currently, with Kinde, you can bring along your own auth pages apart from the ones that are input for sensitive data such as passwords and OTPs. https://docs.kinde.com/authenticate/custom-configurations/custom-authentication-pages/?r=search#_top

We are currently building the ability to customise the HTML and CSS across all the pages - https://updates.kinde.com/board/custom-sign-in-up-page

Or are you after the ability to do the auth flow completely via API?

Screens that remain securely hosted by Kinde

Link to this section
This feature lets you to bypass Kinde’s initial sign in screens, but the following screens are still hosted by Kinde and are part of our secure auth experience.

Enter password or One-time password (OTP) screens (see example above)
Multi-factor authentication screens
The organization switcher (if you support multiple organizations)
The screen where users can choose to create an account if one was not found

and this?