You can see more details of the release in the .NET Core 2.2 Preview 3 release notes. Related instructions, known issues, and workarounds are included in the releases notes. 

EF6 Code First Migrations for Multiple Models 

The previews of EF Core 5.0 require .NET Standard 2.1. This means:

• EF Core 5.0 runs on .NET Core 3.1; it does not require .NET 5.
  • This may change in future previews depending on how the plan for .NET 5 evolves.
• EF Core 5.0 runs on other platforms that support .NET Standard 2.1.
• EF Core 5.0 will not run on .NET Standard 2.0 platforms, including .NET Framework. 

• Delete option is missing from solution explorer context menu in Xamarin Forms Android projects.
• Xamarin.Android: Can't select target framework 28 in Android Manifest settings.
• Could not load file or assembly 'Microsoft.VisualStudio.Web.PageInspector.Loader, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
• "There was an error running the selected code generator" when trying to create a new view.
• Android Berechtigungsliste ist leer-Android permission list is empty.
• Missing icons for .axml files in Visual Studio 2019.
• axml icons are not displayed.
• Visual Studio extensions may fail to install attempting to overwrite core NuGet files.
• C# switch statement on a constant expression may produce bad compiler errors. 

To get started with ASP.NET Core in .NET Core 3.0 Preview 9 install the .NET Core 3.0 Preview 9 SDK.

If you’re on Windows using Visual Studio, install the latest preview of Visual Studio 2019.

.NET Core 3.0 Preview 9 requires Visual Studio 2019 16.3 Preview 3 or later. 

.NET Core 3 will be supported in Visual Studio 2019, Visual Studio for Mac and Visual Studio Code. Visual Studio 2019 Preview 2 was released last week and has support for C# 8. The Visual Studio Code C# Extension (in pre-release channel) was also just updated to support C# 8. 

These are the customer-reported issues addressed in 15.9.7:

• Crashes when expanding variables!.
• /DEBUG:FASTLINK + C7 + PCH crashes debugger.
• Native C++ application crashes because of stack corruption with VS 2017 15.9.2.
• Incorrect Release Mode code.
• Xamarin Unobserved Task Exception WebRequest.
• Link /SOURCELINK option seems to do nothing. This fixes Source Link for Managed C++ Debugging.
• Fixed an issue with corruption of AVX/MPX/AVX512 registers while Debugging.
• Update of Microsoft.VCLibs.140.00.UWPDestkop framework packages for C++ UWP DesktopBridge applications adding support for ARM64.
• Corrected incorrect version of VCToolsRedistVersion in Microsoft.VCToolsVersion.default.props.
• Corrected unsigned embedded dll for VC Redist installers.
• SSDT/Web Tools: We fixed an issue where SQL LocalDB was not installed on Polish, Turkish, and Czech locales.
• SSDT: We fixed an issue affecting SQL Server Analysis Services (Method not found exception when clicking on UI).
• SSDT: We fixed an accessibility issue which was causing the contents of a table not to be visible in the result window when using High-Contrast mode.

Security Advisory Notices

• WorkflowDesigner XOML deserialization allows code execution.
• .NET Framework and Visual Studio Spoofing Vulnerability.