Doing a presentation at a Mac User Group today, I was showing off some POC Mac tricks using a 2005 G4 PowerBook, connected to the video projector via a mini DVI to HDMI adaptor.
With that done I realised I couldn’t connect the MacBook Pro to the projector as I’d left the right adapter at home. I was already sharing the wifi to the PowerBook over Ethernet from the MBP so I went onto settings on the PowerBook and used it to screen-share to the MBP.
I was able to choose which screen to display on the connected projector by minimising the screen share app onto the G4’s Dock, leaving the G4 as the video source. Maximising the screen share app then showed the MBP as the source.
I found the missing USB-C to HDMI adaptor when I returned home.