You don't need to migrate to the cloud. Intune supports hybrid and cloud users. With hybrid configurations you typically use Azure AD Connect. Users must be assigned an Intune license. A special use case is a a device-only subscription service that helps organizations manage devices that aren't affiliated with specific users.
Devices are typically registered in Azure AD, either hybrid domain-joined or as true members. Then they are enrolled in Intune. There are also cases where you do not need to enroll devices and only use App App Protection Without Enrollment. So in some sort or fashion users must exist in Azure AD in order to use Intune.
Microsoft Intune licensing
https://learn.microsoft.com/en-us/mem/intune/fundamentals/licenses