What I see a lot is private Nuget packages with common functionality used within several applications at companies. These are often binaries (one can place code in a Nuget packages but it won’t update, at least not last time I tested it). In the world pre GIT it was common to link in these files and build them along with the solution. Meaning, one did not have to try to align every .NET version or keep adding build targets to the Nuget packages.