SerializableAttribute appears in two namespaces after using NuGetForUnity

To be able to use the package Microsoft.ML, I installed NuGetForUnity (https://github.com/GlitchEnzo/NuGetForUnity). Now I get the following error in many of the files of the UI Core:

C:\Program Files\Unity\Hub\Editor\2019.4.5f1\Editor\Data\Resources\PackageManager\BuiltInPackages\com.unity.ugui\Runtime\UI\Core\AnimationTriggers.cs(9,6): error CS0433: The type 'SerializableAttribute' exists in both 'System.Runtime.Serialization.Formatters, Version=4.0.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' and 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'

I uninstalled the Microsoft.ML package with NuGet, but these errors in about 40 of the files that use [Serializable] in their code remain. I don't know if the errors occured because of the ML-package or because of NuGet.

Thanks for help