.NET Core 3.1 (LTS) was the second long term release for the modern .NET released in December 3, 2019. It was supported for three years, and was the suitable choice for your libraries and appliations.
We have learned that .NET 6.0 was out in November 8, 2021, and that it’s the third long term release for the modern .NET family. This means that .NET Core 3.1 will be out of support soon.
According to this page, .NET Core 3.1 will lose support after December 13, 2022, which is a sign that it will no longer receive any updates, especially the important security updates.
To migrate your project to .NET 6.0, open the project files, and edit the target framework so it says net6.0. When you’re done changing the target framework for every project in your solution, just save all of them, and Visual Studio will reload all the projects with .NET 6.0 as the target.
Unfortunately, if you want to work with such projects that target .NET 6.0, you’ll have to install Visual Studio 2022.
Enjoy!
Aptivi 
Thoughts?