Have you ever used it? Because is doing a "decent" job but not a "great" job. I've been suggested videos that I constantly flag as "not interested" all the time (and since it has no "block" functionality you gotta suck it up if it comes back again)
The algorithm is great but is more about where are you located than anything else. You don't get to see a lot of the content created in the first place just because you're not in the right region (eg. I never saw a Charlie video for example)
Overall I think it might apply a weighted approach on what to show and based on your engagement double down on what you are likely to watch more. Then you've trends, top creators etc that get featured more often.
The only thing I love about TikTok is the non-existing advertising. There's some, but is rather seamless and non blocking that sometimes you are even going to watch it.
Nothing to do with YouTube where you're basically in a worst situation than the classic TV (ads every now and then)