Cast from a local PC on the network. View from a browser with uBlock Origin. I forget that YouTube even has ads most of the time. Using another person's device is always a painful awakening.
YouTube Premium? Paying for YouTube is the best decision I've ever made when it comes to how much time and frustration I've saved per dollar.
Unfortunately, YouTube premium is not available in all countries, so some of us have have to go for more "hacky" solutions if we want to avoid ads.
You might want to consider setting up a Pi-Hole. Not sure how well those work with chromecasts though.
Pi hole cannot block ads inside of YouTube app, only on the web. I suppose that will be similar with Chromecast.
Youtube ads work in a way that domain blocking(pi-hole) cannot block them.
Chromecast uses Google DNS servers ignoring your DHCP DNS. You need to block Google DNS servers on your router so then the Chromecast will switch to your DHCP DNS.
Also, on my experience, some Youtube ads are served through the same domain that serves the video so you won't be completely ad free.