New stuff is scored well too at first, so the algorithm can "test" and see what kind of traction the post gets. If it hits a certain score for traction then it's boosted more, and if it doesn't then it's buried.

It's pretty much purely about the popularity curve of each post. The more it drives engagement the more it's boosted.

All hail the algorithm.

every video starts with 0 views, new videos all get pushed to small sample groups and the ones that get the most engagement in terms of watch time and other factors then get pushed to larger groups

that's the point, the content that doesn't engage users doesn't get promoted. TikTok isn't going to push a boring video to millions of users