Weird. It works fine for me.
The Add-Ons Page says:
Installation: Users with OBS v26.1 or Later
Please note that you cannot use Syphon Virtual Webcam while OBS’s virtual webcam output is running, i.e., after choosing Start Virtual Webcam; trying to do this may lead to unpredictable results including crashes.
Do you have OBS's virtual webcam going at the same time?