I have a Dictionary<string, DemoRecord> with DemoRecord having a field Size.
I now want to calculate the sum of all sizes using LINQ. Here’s the example

public record DemoRecord(string Name, ulong Size);

public class DemoStackOverflow()
{
    public ulong GetSum(Dictionary<string, DemoRecord> data)
    {
        return data.Sum(x => x.Value.Size); // Syntax error
    }
}

However, Visual Studio highlights the Sum method with an error message for which I cannot comprehend the problem.

When explicitly specifying the generic type, it just highlights the data variable with another error message.

Is this impossible? It really seems like a trivial LINQ method. Visual Studio itself suggest that Sum exists on the Dictionary.