Hi @LucianB,
Could you please share more details about the updated fields in App, and the changed user fields, are those fields from the same data source, showing up under the same screen in App?
We could take use of the sendemail function within PowerApps to send the proper notification.
Please take a look at the Office 365 Outlook connection as a reference:
Office 365 Outlook
Check the available functions part.
For the usage, please see the discussion in the following thread:
Send inforamtion by Email
In addition to send the Email within PowerApps, we could also create Microsoft Flow to generate the Email Notification.
For example, if there is an item has been edited, then we could set that up as a Flow trigger, then add a send email action under Microsoft Flow, please first take a look at the template:
When an item in a SharePoint list is modified send an email
If you have any further questions, please feel free to post back.
Regards