I haven't worked on sites as big as YouTube but on sites with 100,000 members who are very much engaged with one "game" you usually find they are mainly indifferent when you offer them another "game" to play.
I like YouTube for what it is. I have interacted very little with shorts but Google has scarily seen into my imagination. I don't want to go into that rabbit hole.
The definition of "similar" is the problem w/ vector search isn't it?
Two populations can be similar in terms of conventional demographics such as age, gender, race, what kind of clothes they wear, etc. but be different in their behavior. IG users are "players of the Instagram game" and TikTok are "players of the TikTok game" and a whole system of values and behaviors are involved.
To take an example playing the "engagement farming" game on Bluesky I can follow people and know some fraction of people will follow me back, but who do I want to follow?
I postulated that the people I want are people who will repost my photos so I can try following people who repost photos but I find that reposters are not "followers" whereas I get a much better response rate if I follow people who follow another social media photographer since those people are "followers". People have an online behavior signature like that which for me matters more than the color of your skin.