MFA and free/legacy plan

We’ve been using auth0 using the free (legacy) plan for testing, and we recently noticed that MFA logins fail.
It also seems there’s a new notification message on the MFA settings page

‘Use of this feature requires the purchase of an addon to your Auth0 subscription. Please contact us with any questions.’

Has this been switched on / enabled recently? Apart from this notice I’ve not been able to find more detailed information about this change.
Further, on the https://manage.auth0.com/#/account/billing/subscription page it’s not quite clear what the Legacy plan now entails. It seems that even though the listing shows MFA as still working, it does not.

With future updates, will these changes find their place on the Deprecations and Migrations page?

The pricing page outlines the features that are available for the Free vs Paid plans:

During your trial period, you have access to paid features in order to evaluate them, however MFA is only available on Developer Pro (paid) plans.