Measurements of multiboson production at the LHC are important probes of the electroweak gauge structure of the Standard Model and can constrain anomalous gauge boson couplings. Recent measurements of diboson and triboson production by the ATLAS experiment at $\sqrt{s} =$ 13 TeV and 13.6 TeV are presented. In triboson processes, the observations of the $WZ\gamma$ and $W\gamma\gamma$ channels are reported. In diboson processes, studies of gauge-boson polarisation and their correlation in $WZ$ and for the first time in $ZZ$ events are presented. In $WZ$ events, these studies have been extended to phase space regions enriched with longitudinal polarisation and the Radiation Amplitude Zero effect is studied.