Unfortunately, this does not work in my case. The problem is not with one browser or another, because I tried several on several devices. I even installed Evernote on new devices, and the problem (repeated name of the same folder) appeared as soon as the new installation has downloaded its dataset, during the first run.
My guess is that the data management system used by Evernote, and in particular the part stored in their central systems (so, not on my smartphone, laptop, or tablet) includes these duplicate entries and allows any form of duplicates to exist. This is consistent with the behavior I noticed on my devices and with the function where you can save say the same webpage multiple times.
Unfortunately, I did not create the same notebook multiple times and do not like this undocumented feature.