Not sure if this will help but according to the site (https://moment.github.io/luxon/#/formatting?id=table-of-tokens) linked to from the Dataview documentation concerning the tokens used for dateformat, the token MMM is month as an abbreviated localized string. It doesn’t necessarily say that the abbreviation matches the number of characters. Good luck!
I’m not sure about your use case, but perhaps you could use substring. After searching elsewhere, I saw many posts within various other softwares where people were having issues with MMM producing Sept. So, I imagine there are definitely workarounds.
It’s not very elegant but I had to divide the date in day, month and year parts stored as items of a list.
For the month part, I’ve formatted it as the month’s full name from which I only keep the first 3 characters using substring().
The list containing each date parts is then joined by "-" to re-create the date.
I’m not very dataview fluent , but this seemed to work from my side of the screen.