Thank you Alexa for reaching out to us!
You can handle this scenario in three different ways. Firstly, as Elfie addressed, you can convert these unmanaged apps to managed apps, and then remove them from the devices. If your devices are supervised, then these unmanaged apps would get converted to managed apps, and then you can delete these apps from the Applications sub-tab of that particular device. However, if they are non-supervised devices, then a device-end confirmation is required for converting these unmanaged apps to managed apps.
Then, you can try the next method. You can whitelist only the required applications, so that rest of the applications will be blocked from the device. If the devices are supervised, then these apps will be hidden from the device. On the other hand, if they are non-supervised, then the device would be marked as non-compliant, thus notifying the admin regarding the presence of the blacklisted app.
And the third possibility is to block the app installation from the App Store.
Hope this answers your query.
Cheers!
Michelle Hendricks
Hexnode MDM