Branes and symmetries for $\mathcal{N}=3$ S-folds

We describe the higher-form and non-invertible symmetries of 4d $\mathcal{N}=3$ S-folds using the brane dynamics of their holographic duals. In cases with enhancement to $\mathcal{N}=4$ supersymmetry, our analysis reproduces the known field theory results of Aharony, Seiberg and Tachikawa, and is compatible with the effective action recently given by Bergman and Hirano. Likewise, for two specific $\mathcal{N}=3$ theories for which Zafrir has conjectured $\mathcal{N}=1$ Lagrangians our results agree with those implied by the Lagrangian description. In all other cases, our results imply novel predictions about the symmetries of the corresponding $\mathcal{N}=3$ field theories.