A DNS sinkhole cannot block YouTube ads. If you manage to block one of their ad-serving domains by a lucky guess, they will just deliver the ad content over the same domain as the real video's content. Blocking YouTube ads is beyond the capability of a DNS-blocking solution. I'm sure Google has an army of people preventing ad-blocking, and sinkholing domains is not good enough. You need a content blocker, such as uBlock Origin on the desktop, or a third-party YouTube app on your device (such as NewPipe):
https://f-droid.org/en/packages/org.schabi.newpipe/
You will not be able to block ads if you cast them to a Chromecast; it's not possible. Unless you find some kind of third-party casting that is capable of running a third-party YouTube app.
Long discussion here:
https://discourse.pi-hole.net/t/how-do-i-block-ads-on-youtube/
Privoxy can and will content filter, however only http domains. And with the recent trend towards https ad serving, Privoxy is slowly but surely becoming obsolete. Don't even waste your time trying to setup Privoxy if your intention is to block YouTube ads.