I just upgraded from a galaxy S10+ to a S22 Ultra and when I try to watch YouTube videos in 2160p it only gives me 1080p. I went to the same video on my old phone and my old phone gives me the 2160p option.
Some videos aren't available in 2160p. There have also been changes on YouTube over the past year or so that makes 4k only available to certain accounts / devices. I'm not sure what the causes of why some accounts just don't have 4k available, but the thought is they're going to make it exclusive to premium users due to their bandwidth costs (they've already introduced high-bitrate streaming for premium users). My last recommendation is simply reinstalling the YouTube app.
