You’ll find that folks can be gullible at any age. My step-kids, who live with their dad in Texas, are in their early 20s and get about 99% of their information from either YouTube or TikTok. For the youngest, church plays a big part. Generally speaking, they are good kids, but they are both gullible AF. I’m betting OP’s sibling has a similar diet of media consumption.
Not to mention the entire premise of the post being, essentially, "I don't approve of the entertainment my sibling chooses to consume. Please make suggestions for me as to other entertainment that I can then use to regulate said adult sibling, removing their entertainment that I don't like and forcing them to consume something I find more acceptable."
Like...I think Rogan's whole thing is stupid and most I've talked to who like his stuff are similarly ridiculous...but to go from that to full out "I plan to take it away from them and force them to do something I find more acceptable" is really quite a leap.
Or maybe it's "I love my sibling and don't want to see them slip further into this conspiracy rabbit hole. How can I offer them similar content that isn't as harmful?"