Review on 🔌 Cable Matters 3 Feet 4K Mini DisplayPort to Mini DisplayPort Cable - Black | Not a Thunderbolt Replacement | Non-Compatible with iMac & Target Display Mode by Jason Ingram

MacBook Pro 2015) is the cable you need. It took me a while (and a few failed attempts with other cables) to find this one and it works great. You can toggle (using the F2 command on your iMac) to switch between an external (and extended/dual) monitor for your MacBook and the iMac's home screen (for use as a standalone iMac or a multitasking app on your iMac), while you're doing something else on your MacBook). VERY practical and helpful. And this cable is great for the job. [Caution: If you have a more modern iMac and/or MacBook, you probably only need a Thunderbolt cable, but for older versions, this is the ONLY thing that will work.)