Just saw the notification for this in my Youtube Studio. For now it seems as if this setting is turned off by default, but for anyone like myself who uploads videos to Youtube, I recommend checking that they don't decide to toggle this on for you in the future.
Its not surprising. Youtube now has standing to sue other models for scrapping their information while also making it exclusive to third party consent - there is no toggle visible for google using to model ai.
This is them making it explicit that only they can use youtube, especially given how it has shown to be a great asset in putting them ahead with the text to video.