I have a MacBook Pro 15" (Late 2016, Touch Bar and USB-C ports), and I want to sometimes use the screen as a monitor for my Raspberry Pi. I know that old MacBooks couldn't do this because the HDMI port is HDMI-out only, but USB-C seems like it should be able to be used as both input and output? Anyone have any ideas on how I can use this screen as a Raspberry Pi monitor? I have an HDMI to USB C adapter that I use for HDMI output on this MacBook, but no idea if that works the other way around.
Can Macbook Pro (Late 2016, USB-C) screen be used as monitor for Raspberry Pi over USB-C with HDMI adapter?
No. Even though the USB-C plug is the same on both ends, the MacBook Pro can't act as a display. You'll need to use remote desktop software like VNC if you want to see the Raspberry Pi's desktop on your laptop.
Target Display Modewhich "lets you use the built-in display on a supported iMac as an external display for another Mac.". According to available information, this works only for a few iMac Models. I never read about new MBP, that support this feature. If both, the RPi and the Mac are in the same network, you could use VNC, x11 forwarding, etc.