Higgs-boson decays to two photons can be selected with high efficiency and the very good
invariant mass resolution allows a robust subtraction of the backgrounds. This proceeding presents
measurements of Simplified Template Cross Sections, differential and fiducial cross sections, as
measured in the diphoton decay channel by the ATLAS detector using the full Run 2 data set of
proton-proton collision data collected at 13 TeV at the LHC, and their interpretations in the context
of an Effective Field Theory