I have downloaded and installed .NET Core 5.0 SDK (v5.0.100-preview.1) in my Visual Studio 2019. But it is not available in Target framework. Am I missing something?
You need to install the latest preview of Visual Studio 2019 16.8, refer to
https://devblogs.microsoft.com/aspnet/asp-net-core-updates-in-net-5-preview-1/
You also need to explicitly enable preview versions within Visual Studio itself:
Then you should see it: