Windows 10 19H1 preview build 18277 is now rolling out to the Insiders in the Fast and Skip Ahead Ring with some notable improvements. This test build improves Focus Assist feature, Action Center, Emojis and more. Microsoft is also adding a new feature to the Action Center that would allow you to customize the quick actions right from the Action. Action Center is getting better with Microsoft finally adding a brightness slider. Microsoft will enable the advanced DPI settings by default to automatically address scaling problems experienced on some systems.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-19h1-build-18277-is-now-available-with-action-center-improvements/