The bug
When starting Minecraft, the main menu fades in after the game is loaded. However, the language button as well as the accessibility button no longer fade in. This was not the case in 1.14.4.
How to reproduce
Launch the game
Look closely at the accessibility options button
I am not entirely sure about this happening in 1.16-pre2. The buttons appear before the rest of the menu, but I would say they actually fade a little. I'd appreciate a second opinion.