I think the best solution right now for older Chromecast (ones without a dedicated remote) is running castblock on a raspberry pi or something else attached to your network. It doesn't block ads but it can automatically mute the chromecast volume when ads are playing, as well as automatically hit the skip button when it shows up (maybe like 5% of the time it misses both but still better than nothing). It also looks up sponsor segments from sponsorblock and detects when a sponsor is about to play and can skip those too. It auto detects all Chromecast on the network so all you have to do is run the program with the flags for what features you want enabled / what sponsorblock segments it should skip.
If you have a Chromecast with Google TV (with like a remote control and apps) I've heard smarttube-next is a good alternative app with ad blocking.
I'm not sure what works with TVs that have Chromecast built in, might also be smarttube-next. I only have the Chromecast ultra and the older standard Chromecast and castblock works great running on my pihole box