The nuget configuration object is used to control settings for the NuGet package manager.
The NuGet package manager supports a SDK-style .csproj/.fsproj/.vbproj/.props/.targets format, as described here.
This means that .NET Core projects are all supported but any .NET Framework projects need to be updated to the new .csproj/.fsproj/.vbproj/.props/.targets format in order to be detected and supported by Renovate.
The NuGet manager also supports global.json and dotnet-tools.json SDK files.