Closing the Mass Window for Stupendously Large Black Holes

We show that primordial black holes (PBHs) in the $\mathit{\text{Stupendously}}\mathit{\text{Large}}\mathit{\text{Black}}\mathit{\text{Hole}}$ mass range ($M\gtrsim {10}^{11}{M}_{\odot }$) produce isocurvature perturbations exceeding current $\mathit{\text{Planck}}$ Cosmic Microwave Background limits, thereby excluding them as a significant dark matter component.