It does appear that https://www.youtube.com/c/OERProject/videos are CC-BY-3.0, though none of the other material seems to be. Naive searching doesn't turn up any of the videos or material extracted from them on Wikimedia Commons or archive.org but maybe that'd be a useful project.

Added: the Gates Foundation did (and may still for all I know) provide funding to some OER projects 10+ years ago, also to Creative Commons on the idea that organization was infrastructure for OER or something like that. I'm not really suprised if they've focused on getting schools to adopt whatever they are funding, really open or not, since then; it sounds like they've had some success. If there's a trove of under-exploited openly licensed educational videos linked above based on that engagement, and/or based on YouTube adding the ability to opt into CC-BY-3.0 licensing sometime before then, I'm mildly satisifed.