Thanks for that, I was at a similarly state 😁!
So I wasn't wrong with my code.
My current problem is to identify the layout-instance inside the wpf-control.
But I think I got it (with your example):
The "PropertyPage1ViewModel" will be instantiated by Pro, Data[0] will be set to the layout-instance.
Then the custom-control "PropertyPage1View" (User-Control) ist created. After the constructor (not at it's end!) the DataContext-Property will be set to the the instance of the view-model.
The next step is to find out, how I should write and read the settings with the module "OnReadSettingsAsync/OnWriteSettingsAsync" (best practice).