The SharePoint integration is specific to the List form functionality.
I'm puzzled, for the test app, did you generate from data or start from blank? It seems like it should work.
For the test app, I created a new Canvas Power App, using the same SharePoint list. I have a duplicate copy of the SharePoint list setup in Classic Experience (For InfoPath)... I might try that one on Monday , and create a new Canvas app and connect to that copy and see what it turns up with. Will post my results.
I am also just going to create a app with no connection to SharePoint and try it as well...