This is also an issue for Nintendo Switch (adding because it just says XBox on the ticket); only the 1st player can see the end crystals and the dragon.
As the 2nd player, I was able to defeat it by shooting just above the flames of the end crystals to destroy them and then waiting for the ender dragon's shadow to appear on the bedrock pillar and swinging with my sword at the area above it. The purple breath wasn't insta-killing (and was visible) which was nice, so it was just annoying that the dragon and the crystals were invisible.
This only started when we upgraded to 1.16.
Same - immediately get a screen saying "Level export failed".
Login issues still abound on Switch. Hotfix seems to have fixed crashing for me which is nice but the integration with online features like MS Account, Realms, Servers, and Marketplace are all broken.