Source: https://www.androidcentral.com/google-mistakenly-teases-android-11-before-taking-down-preview-page
Some of the features listed include:
New security features
APIs for foldables
APIs for sharing
APIs for Vulkan
and more
The page was quickly pulled, but it is speculated that they may be releasing a developer preview soon as the page looks ready to go live, although none of the links functioned.