Make sure you’re also blocking all other outbound DNS at your firewall. Many “smart” devices (and presumably some apps, though I have no way to check this) are hard coded to use 8.8.8.8 regardless of what DCHP says to use.

I see a lot of people saying “but that’s how creators get paid”.

Listen: I didn’t put ads on my video. YouTube did. I can’t take them off and I don’t see a cent from them. Block away.