https://www.bleepingcomputer.com/news/microsoft/microsoft-announces-end-of-life-for-multiple-net-framework-versions/

Microsoft today announced that multiple .NET Framework versions signed using the legacy and insecure Secure Hash Algorithm 1 (SHA-1) will reach end of support next year.

The .NET Framework is a free software development framework that helps developers build .NET applications, websites, and services and users to run them on many operating systems (including Windows), using different implementations of .NET.