Why is typeof((int A, int B)) allowed while typeof(string?) is not?

[jnm2]

typeof(string?) and typeof(dynamic) are compiler errors. Isn't the reason for this that the syntax contains extra information that can't be represented in the resulting System.Type instance, over and above typeof(string) and typeof(object)?

If so, what about the extra information in typeof((int A, int B)) that can't be represented in the resulting System.Type instance? I would have expected the only options to be typeof((int, int)) and typeof(ValueTuple<int, int>).

(SharpLab)

[RikkiGibson]

See Warn when "attribute-dependent" types are used in 'typeof' dotnet/roslyn#54804