I would like to create a PowerApp for Dynamics 365 for Customer Engagement that is for a specific business unit of people.
So for each business unit they would have their own PowerApp. Can I limit the app to a specific business unit within one instance?
Could you please explain a bit for the "a specific business unit of people" here?
PowerApps Environment and Dynamics 365 customer engagement instance now should be the same, which means if an Environment created in PowerApps, then a corresponding instance would appear in Dynamics 365 Admin center.
If here you would like to have the App created within one instance, then please consider just holding them into one Environment.
For Environment management, see: