Getting MatrixPropertyDistribution::sclrvctr: error from documentation example

I’m new to StackExchange, but I am having a strange error using just downloaded Mathematica 12.1.1.0 (Student version). I’m trying to use the MatrixPropertyDistribution function, but Mathematica gives me an error even when I use the exact example that it gives in the documentation: https://reference.wolfram.com/language/ref/MatrixPropertyDistribution.html.

In particular, when I try to copy and paste the first example and try to run it,

Mean[
  MatrixPropertyDistribution[Tr[x.x], x [Distributed] 
    GaussianOrthogonalMatrixDistribution[2]]] // N 

I get the error:

MatrixPropertyDistribution::sclrvctr: Tr[x. x] should be a scalar or vector expression.

Even if I do the expression:

Mean[
  MatrixPropertyDistribution[1, x [Distributed] 
    GaussianOrthogonalMatrixDistribution[2]]] // N 

I get the absurd sounding error

MatrixPropertyDistribution::sclrvctr: 1 should be a scalar or vector expression.

What is going wrong here?