Connecting two MacBooks over USB-C for transferring video signal from one to the other I have two MacBooks (a Pro and an Air).  Both are modern and have USB-C.
I would like to run the video output from one MacBook into the other, using USB-C, and then use the second Mac to stream the video using OBS.  Is this possible without putting some converter in the middle?  It feels like it should be...
No, target display mode doesn’t work over USB-C.
You’ll want to screen share over point to point network for this.

https://www.airsquirrels.com/airparrot/

The latency for screen sharing is very good now. You might have better luck with an iPad for this and sidecar or dedicated hardware to get it into OBS.

https://shop.astropad.com/collections/luna-display-mac-and-pc