How do you disable Ambient mode?
I have successfully disabled Ambient mode.

... by turning on Google Assistant and then turning off all the options (including Ambient mode).

The Google Assistant options can be reached (on my phone at least) by traversing: Settings | Google | Account Services | Search, Assistant &amp; Voice | Google Assistant | Assistant (tab) | Assistant Devices | {choose your device}.

I'd like to see Assistant off -> Ambient off, but for now it's a solution...