A search for axion-like particles (ALPs) decaying into diphotons using the ATLAS detector is presented. ALPs, hypothetical light particles potentially part of a hidden sector, are investigated in the context of Higgs boson decays. The study focuses on a Higgs boson decaying to a $Z$ boson and an ALP, with the $Z$ boson decaying leptonically. For prompt ALP decays, a dedicated analysis targeting events with two leptons and two collimated photons (either merged or resolved) has been completed and published. Ongoing studies examine scenarios where ALPs are long-lived and predominantly decay within the calorimeter volume, resulting in displaced photons that require specialised identification techniques. This proceeding summarises current findings and future prospects of these ALP searches.