The algorithm is pretty simple, it'll show you a selection of videos that are from the n most popular genres of videos, then depending on your dwell time, it'll A/B test categories that are related, or sub categories.

That bit isn't that difficult or new. the special sauce is the editorialising and content categorisation. being able to accurately categorise videos into genres, subjects and sub subjects (ie makeup video, 25 year olds, woman, straight, new york, eyeglitter) and then creating a graph of what persona likes what.

The second secret sauce is people going through and finding stuff and promoting it. TikTok (used to) editorialise/pay highly for content.