Sounds like a smart kid, is part of you secretly proud of him for his tenacity?

Is it impractical to keep an eye on what he's doing on his computer, i.e. physically checking in on him from time to time?

How about holding him responsible for his own behavior, to develop respect for the rules you impose? Is it just hopeless, and if so how come? Is it impossible for him to understand why you don't want him watching certain content or why he should care about being worthy of your trust?

I'm not judging here, I'm genuinely curious.

Personally I wouldn't want to expose a child to "the algorithm" ie recommendations. It turns up useful stuff but (IMO) the stream contains an unacceptable concentration of radioactive waste and becomes increasingly concentrated if you click on any of it.

I might suggest explaining this to him, providing a uBlock filter to sanitize the page, and requiring use of said filter.