What’s wrong is that SDP constraints must be affine, but t is not affine. CVX only accepts SDPs which are LMIs: Linear Matrix Inequalities. The matrix appearing in an SDP in CVX must be a linear (affine) function of CVX variables. Norm is not linear.
The semidefinite constraint is (reformulatable to be) convex in one dimension (N = 1), but I doubt it is in dimension >= 2. I will assume it is not convex unless you prove it is,