So I just came across another one of Microsofts seemingly arbitrary limitations in using policies to manage Windows 10. This one is another example where there is a policy setting that only works if you have Windows 10 Enterprise or Education editions and not for Pro.
If you want a policy to lock down the Windows Store to only show applications in your organisations Store then you are going to be out of luck…
https://docs.microsoft.com/en-us/microsoft-store/manage-access-to-private-store
If anyone knows a way to block the Windows Store for Pro editions I would be interested to hear from you.