Syphon stopped worked with 10.14, so for most macOS users this will not be the way to go. In modern macOS and OBS, you use the "macOS Screen Capture" source built-in to OBS, use the "Window Capture" method, and choose the veadotube window. You then add a "Filter" and choose "Chrome key" and you're good to go.
Heh, I wonder if the Syphon update I was reading meant macOS 14 (or I just messed up), but yeah, things have changed for newer macOS versions. Both the information you shared and the information I shared will be useful to anyone using macOS, use whichever one fits your situation. I'm on 15.1.1 and Syphon absolutely no longer works, but the built-in "macOS Screen Capture" does.