Prevent supervised devices from installing Apple beta software
Use Apple Configurator or Mobile Device Management (MDM) to prevent the installation of Apple beta software on supervised devices.
iOS beta software is available to users who enroll in an Apple Beta Software Program.
You can prevent users from installing beta software on supervised devices through Apple Configurator or an MDM solution.
In Apple Configurator, open the iOS Restrictions payload window.
Deselect "Allow installing configuration profiles (supervised only)."
If you use a third-party MDM solution, look for the key "allowUIConfigurationProfileInstallation".
When you set this restriction, users can't install profiles from email messages or websites. This includes the profile that enrolls the device in the iOS Beta Software Program. It also prevents users from enabling beta updates in Settings. You can still use Apple Configurator or MDM to install profiles on the devices you manage.