I have a Pi3 with multiple Oses one of them of which is Window IoT Core. I see that there is a remote client for Windows but is there anything for MacOS??
Unfortunately this is not compatible with a product of Apple. Even with a Windows 7 PC you'll not be able to install the remote client. One and only possibility is Windows 10. I would recommend you to run a virtual windows 10 on your MAC if you want to use your RPi with Windows 10 IoT.