The aam_backend_login widget is unavailable since version 7.0.4.

[joopmartens]

After upgrading to version 7.0.4 or 7.0.5 the aam_backend_login widget seems to be unavailable.

Instead of the login fields an error is shown:

Error: Your Requested widget "AAM secure login " is not in the widget list.

Also the following report does not show an available widget:
https://plugintests.com/plugins/wporg/advanced-access-manager/7.0.5

While in the report of version 7.0.3 it is still available.
https://plugintests.com/plugins/wporg/advanced-access-manager/7.0.3

Reverting to version 7.0.3. solves the issue.