GDB from Framingham Said:
"Can a Mac mini be set up for two concurrent users?: I was wondering if a Mac Mini can be first set up with 2 partitions, install the OS on both partitions, then run two different users, with two separate monitors and keyboards, at the same time? Or set up in any way so that my wife and I can share the same Mac mini with two separate monitors in two separate rooms. Basically time-sharing."
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Running Concurrent Apple IDs On a Device:
No. You can only have one Apple ID assigned to an Apple device. Your device has a Serial Number, which is what all signed in Apple Accounts refer to.
Use of a Virtual Machine (VM):
Granted, as a workaround, you could run your second Apple ID on your Mac through use of a Virtual Machine, while your Mac is running in the background. All would be accessed and would operate as desired on the VM. Virtual Machine applications are VMWare Fusion and Parallels. Regardless, you cannot access both purchases between the Virtual Machines even. Learn more here: What Is a Virtual Machine? - VMware Support.