You can view the changes made to the default new React Native Windows applications for C++ and C# using React Native Upgrade Helper. See this document for more details.

What's New

PackageReference for C++ projects: New C++ projects use recently added MSBuild support for PackageReference based NuGet restoration. This change lays the foundation for simplified build logic, smaller downloads, and always up-to-date references to libraries (such as the RNW NuGet package).
Native animation driver improvements: There have been many improvements to the native animation driver, around both correctness and reliability.
onMouseEnter/onMouseLeave on arbitrary native components: We previously exposed onMouseEnter and onMouseLeave callbacks on <View>. These are now exposed to all native components (e.g. <Text>).

-onDropViewInstance API addition: We've created the onDropViewInstanceAPI to enable view managers to track when a view has been removed the shadow tree.

editable support for <TextInput> with secureTextEntry: <TextInput> components that are marked as secureTextEntry now correctly respect the editable prop.
Debug variant NuGet packages: We now publish binaries for the debug builds of Microsoft.ReactNative, that can be used in place of the default release-mode binaries. E.g. by using the Microsoft.ReactNative.Debug Nuget package in place of Microsoft.ReactNative.
run-windows architecture selection: run-windows previously would always default to building x86 applications. It now defaults to the system architecture (e.g. x64 or ARM64).
Automatic PCH selection: We've enabled large PCH's by default on machines with more than 7GB of memory per-thread. This can help to significantly reduce build time on pools with high-memory hardware.
Other bug-fixes and improvements: We've made many more fixes across the platform. Expect less crashes, more correct behavior, and quality of life improvements for developers.

-Support for WebView2 control via react-native-webview:We've enabled the use of the WinUI WebView2 control via the react-native-webview community module for React Native Windows apps that use v0.68+.

Breaking Changes

packages.config projects: Projects using packages.config, either directly, or transitively through community modules, may need to be modified. run-windows, and Visual Studio using the default project, restore both packages.config and PackageReference dependencies, but you may need to restore packages.config projects explicitly if using MSBuild directly. This requirement may be removed before the final release of RNW 0.68.
Node 14: react-native 0.68 now requires Node 14 or later to be used.