When setting up a new device, one of the setup screens will ask the user to sign in with an Apple ID:
Signing in with an Apple ID during device setup is necessary in order to use features like iCloud services and the macOS App Store.
Fleetsmith doesn't create new Apple IDs for users. Employees can use their personal Apple ID to sign in or create a new Apple ID using their company email address.
With Apple Business Manager-enrolled devices it's possible to hide the Apple ID setup screen if you prefer that users don't sign in at all.
This can be configured at [company-name].fleetsmith.com/mdm/configuration.