Microsoft Wireless 900 Desktop and iMac running 10.11.6 Will this desktop setup work with the iMac running 10.11.6?
It &quot;should&quot; work.  From the technical specifications page:

Computer
Requires a PC that meets the requirements for and has installed one of
these operating systems:

Windows 10 / 8 / 7
Mac OS X v10.4 – 10.7


It's just an USB HID (Human Interface Device).  Now, there may be certain keyboard/mouse functions that are not available due to the limited availability.