Maybe I was using it wrong? As I recall, "the usual" APIs present in most other OO languages were not available when I tried to help a friend with a project 3 montjs ago.
Which collection APIs were you missing? Between the standard interfaces and their default implementations[1] and the extension methods to IEnumerable[2] you can do quite a lot in my experience.
You might've forgotten to reference LINQ and Collections.Generic in your project? Because C# definitely has good collection APIs that influenced many languages including Java Streams.
[1]: https://docs.microsoft.com/en-us/dotnet/api/system.collectio...
[2]: https://docs.microsoft.com/en-us/dotnet/api/system.collectio...