.NET 5 would be the best option moving forward. Most new courses will be built against that standard, and it's been out long enough from Microsoft. We are supposed to get .NET 6 later this year.

Specifically, .NET Core 2.2 is "out of support" per the page Mike Woodring shared. .NET Core 3.1 is the latest LTS version of .NET Core and .NET 5 is the latest version of .NET. For other projects, I just recommend using the Bash install scripts (https://dotnet.microsoft.com/download/dotnet/5.0) to install both .NET Core 3.1 and .NET 5 side-by-side to cover all bases.

Please support .NET (Core) 5 - that is the stack that will be used by all courses being developed as part of the core C# skill paths that are currently the process of being updated. Specifically, .NET 5 (formerly called .NET "Core") as shown on the left of the following page, .NET Framework 4.8 that's shown on the right.