Intune is a cloud service and it cannot be run as a standalone on-premises. While cloud services maybe the desired solution for most, ConfigMgr is not going anywhere. Atleast not in the immediate future. I believe there are can be various options available to meet your requirements. You can consider VPN tunnel to secure your endpoint traffic amongst other things. Consider speaking to Microsoft or an MSP.
Can intune be run on-site for use with air gapped networks
At my company we have been using System Center Configuration Manger (SCCM) and Microsoft Endpoint Configuration Manager (MECM) for managing our user endpoint machines. The network we work on has to be air-gapped for security reasons, so these tools have been sufficient up to now.
However, it seems as though Microsoft is really pushing companies to adopt Azure, and the writing is on the wall that they'll deprecate SCCM and MECM soon. Even the new MD-102 Certification has whole sections in it about Microsoft Intune, and no other solution that I am aware of.
So my question is, is there a version/fork/configuration for Intune that would allow it to run on-site on our servers so it can be used on a air-gapped network?