For anyone who found that the 'Classic Policies' was blocking them from activating security defaults, even if they had no Classic Policies or had manually disabled/removed them, you may find that it works now.
I was advised by our Azure support agent that a bug had been identified during a call earlier this week, with an fix ETA'd for today (Fri Jan 24, 2020).
I tried again today and was able to successfully enable Security Defaults (with automatic disable of Security Baselines).
For anyone who found that the 'Classic Policies' was blocking them from activating security defaults, even if they had no Classic Policies or had manually disabled/removed them, you may find that it works now.
I was advised by our Azure support agent that a bug had been identified during a call earlier this week, with an fix ETA'd for today (Fri Jan 24, 2020).
I tried again today and was able to successfully enable Security Defaults (with automatic disable of Security Baselines).