In 2017, Microsoft introduced a new MS Build project file structure for .NET. The previous format dated back to 2003, when .NET 1.0 was released.
The new (well, not anymore) format is way less verbose, and the old format does not support .NET core/standard or .NET 5.0+.
Note that all rules of DotNetProjectFile.Analyzers do not support the legacy
MS Build project format. So also from that perspective, it is better to update.
Further read: https://natemcmaster.com/blog/2017/03/09/vs2015-to-vs2017-upgrade/