I believe from my research that, of the various ArcGIS field apps, public offline forms are only available from the Survey123 app.
Is that correct?
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There's ArcGIS QuickCapture too, but only if the creator has upgraded their ArcGIS Hub Basic licence (included in AGOL) to Hub Premium (c.GBP1k-1.5k I believe).
ArcGIS Field Maps app doesn't support it.
ArcGIS Collector (superseded by Field Maps) does not support anonymous access (= no public access), and GeoForm does not work offline.