Can't create embedded canvas app for Power Apps, not found in tenant

Question

I have an model-driven app. Trying to extend with Canvas Apps.

I follow instructions for creating (https://learn.microsoft.com/en-us/powerapps/maker/model-driven-apps/embedded-canvas-app-guidelines#enable-an-embedded-canvas-app)

I tap 'Customize' to generate the PowerApp but keep getting this error message:

Have tried all browsers.

Using the classic designer was failing me, so I tried the updated viewer.

Never creates.

Another error message:

Edge:InPrivate