Since upgrading to iOS 13 (any version, including iPads), YouTube (the website) refuses to AirPlay video. It only projects audio. I’ve had to revert one of my devices to 12.4.1 (before Apple decides I’m not allowed to use it anymore) to restore this functionality. Invidious would be a suitable alternative, but its support of AirPlay is broken. I assume that since AirPlay of video works across other websites that this is a Google problem, but good luck getting them to fix anything.