SOLVED - SEE BELOW.
We have 2 beautiful 65" LG OLED TVs and have switched from DirecTV to YouTubeTV, using the new Google Chromecast dongle. We can use the app built into the LG tvs - and it looks really good. OR we can use the new Chromecast dongle with the nice little remote and have a picture that is dark, reddish, blocky, pixilated, inferior. Often poor, almost always not very sharp and dark.
Our home wi-fi uses the Google Mesh system, and neither TV is more than 20' from the nearest router. The internet coming into our home is 300MB fiber optic.
SO - we have these new, inferior Google Chromecast YouTube TV dongles that nicely pull everything together, but deliver a really inferior and often crap picture. We complained about the first adapter and after a LOT of troubleshooting, they sent me a new one. SAME problems! What is YOUR experience, compared to what you used before this new hardware?
SOLUTION:
Match content frame rate is under the Chromecast settings under Video.
So long-press Home, Settings, Display and Sounds. Make sure that "match content frame rate" is selected!
That completely fixed the bad video on my LG OLED tvs!