I removed the Newtonsoft.Json-for-Unity asset (GitHub - applejag/Newtonsoft.Json-for-Unity: Newtonsoft.Json (Json.NET) 10.0.3, 11.0.2, 12.0.3, & 13.0.1 for Unity IL2CPP builds, available via Unity Package Manager) in favour of the com.unity.nuget.newtonsoft-json package as recommended by the author.
Now i got the package as part of my project, but the namespace is no longer found in Assembly-CSharp, which totally makes sense, because the package is not referenced in the project.
How do i add a reference to a dll from a package?
I know the question sounds really really stupid because its a thing that should be really standard and done automatically or within seconds. It is done automatically with other packages like TextMeshPro.
I did the whole clear caches, delete temp files, delete and recreate projects stuff as recommended when you google it.