ContentID is generated internally by Google and you have to qualify (aka be able to threaten Google with lawyers) in order to effectively participate. It also seems to be defeatable by such advanced techniques as flipping the video left to right.

If SynthID works, this would allow people to tag their own videos with a watermark that is invariant across various levels of compression and editing. It would enable automated scanning of YouTube videos for uploads and the consequent class-action lawsuits.

Because of that, I can fairly confidently say that this doesn't work. However, it will function to divert some attention for a while. And that's what Google and OpenAI intended in the first place.