It appears that the synchronization with amazon S3 is always total.
I add a post and during the synchronization, more than 14000 files are transferred, that is to say all the html files, images, … The file files.publii.json is not transferred to S3 during the synchronization.
I am obviously not the only one to suffer this problem (see https://github.com/GetPublii/Publii/issues/1051).
I thank you in advance for correcting this anomaly.
I would like to add that the penalty is not only in terms of synchronization time, but also financially because S3 charges for the movements on the files. In my case, instead of affecting a few dozen files each time, it is more than 14,000 files that are impacted. Hence the cost!