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There is the document for all the capabilities that are available now: App capability declarations.
You can see that currently, there is no capability called applicationViewActivation. This means the capability is not available for the public or the capability is removed.
For another capability, it should be inputInjectionBrokered now. It's a restricted capability. You may request approval from the store team for this capability in your app if you want to submit to the Store.
This capability is used to allows apps to inject various forms of input using InputInjector Class. You could refer to this document Injection which contains a sample code snippet that implements the function.
For the second question, there is no way to embed other application's views into UWP apps based on the API available for the public.
Thank you.