I use a 1080p monitor and what I’ve noticed is that once creators start uploading 4k content the 1080p version that I watch on fullscreen has more artifacting than when they only uploaded in 1080p.
Did you notice that as well?
Watching in 1440p on a 1080p monitor results in a much better image, to the detriment of theoretically less sharper image and a lot higher CPU usage.
YouTube compresses the shit out of 1080p content. Any video that has a lot of movement will look like trash at 1080p. Even if you’re on a lower resolution monitor, the higher bit rate of higher resolution videos will look better. It’s all very stupid on our end, but I assume it saves them a ton on bandwidth.