There is a complete new set of alert sounds to choose from in System Preferences once you update to macOS Big Sur. These new sounds were created using the old ones. Also, learn how to save the old sounds now, so you can use them again in Big Sur.
A new feature of macOS Big Sur is Control Center. This is an iOS-like feature that brings together various system controls like volume, Wi-Fi, Do Not Disturb and other settings into a single panel you can access with one click in the menu bar.
The new macOS Big Sur coming out this fall will have a fresh new design and look quite different than macOS Catalina and before. While it is still early in the beta cycle, take a look at the design elements in Big Sur.