I've tested the new Chromecast with Android TV built into it. The one that has its own little remote. It was not comfortable for me to watch and caused some eye strain. Text is hard to read and I get the sensation my eyes are pulling apart.
I have no issue with the old 1080p Chromecast. I did have issue with the older Nexus Android TV. So its possible something Android TV does.
I bought it as a Christmas gift for a family member who has an older curved 4k Samsung TV.
This TV has older generations apps on it that are out of date and no longer supported. So the New chromecast is perfect to make the TV smart again.
I had no eye strain issue with the old youtube app or a ps4 plugged into this same TV. So I can confirm its solely the Chromecast with Android TV doing strange stuff. It might be doing some upscaling as the TV always reports a 4k resolution even if you are playing 1080p content.