If it isn't AI it would probably some other awful right wing shit. The algorithm is manipulated and him being on this path is catered due to his watch history. You can blame AI+YouTube, but also have you talked to him about the content? "Dad that story wasn't real, I found it on the internet and it's made up. And I just looked up this one and it also isn't real. Can I help you find better YouTube channels to follow? There's a lot of good content but it can be hard to find without a bit of help."

Maybe he won't be receptive to content suggestions, but nobody else going to try to improve your dads life.

Good luck.