Presented is the search for anomalous Higgs boson decays into two axion-like particles (ALPs) using the full Run 2 data set of $140\,\text {fb}^{-1}$ of proton-proton collisions at a centre-of-mass energy of $13\,\text {TeV}$ recorded by the ATLAS experiment. The ALPs are assumed to decay into two photons, providing sensitivity to recently proposed models that could explain the $(g-2)_\mu $ discrepancy. This analysis covers an ALP mass range from 100 to $62\,\text {GeV}$ and ALP-photon couplings in the range $10^{-7}\,\text {TeV}^{-1}