Other release dates mentioned online include Ireland, Iceland and the UK on September 17.
The French reveal mentioned may have been originally sourced from IMDB, but the Australian date is a mystery as that page currently lists October 1 for Oz.
It is worth pointing out that the 15th of September is a Wednesday and the 16th is a Thursday, though Wednesday openings and Thursday preview screenings did used to be fairly normal occurrences pre-pandemic.
A series of tweets and info online has implied that Dune may premiere as early as September 16 in Australia and at least a little earlier in France, with a date of “15/9/21” (Euro dates, amirite?) listed there.