Doesn't work anymore. YT absolutely hated users doing so, and since last year it can turn on monetisation regardless of your own choice. It's not automatic (yet) but let's not act like they will see a channel with multiple millions of views and let it rot. Vtubers doing ASMR has been complaining about their videos having ads, even though they explicitly set it otherwise, as it ruins it for VOD watchers without adblock
Edit: It's not exactly verifiable, but I believe it was mostly speculated to be triggered by history and generally educational channels, who did not monetize their content out of principles