31/11/2021 is quite ambiguous, I can’t find such a date on my calendar, by either notation.
I’ve scheduled cron jobs for February 31st, to have them tracked but disabled.
You're making the assumption that users know YYYY-MM-DD is the date format and not YYYY-DD-MM. I bet if you asked non-developers the answers you would get would be pretty random, probably more errors than the locale on their machine.
the point is, no program writes the date YYYY-DD-MM (or at least, it's very rare).
users who don't know what ISO 8601 is would learn, simply because when that format is used in software, it is consistent!
> YYYY-DD-MM (or at least, it's very rare)
Wikipedia claims [0] that is the date format in Kazakhstan, but only for the Kazakh language, not for Russian. (Maybe there is someone here from Kazakhstan who can confirm if that is true or not.)
A lot of companies don't have any employees in Kazakhstan (which means they can ignore this for internal systems); and many companies wouldn't have any customers there either (which means they can ignore it for external systems as well).
Even having been told that there's a difference, you cannot know which is which.
Even if you think you know because you found an unambigious date like 31/11/2021 somewhere, you still shouldn't be confident because there are many sources of dates, and they're formatted by many different pieces of code. Some may be doing the "right" thing, some may be using US formatting. A complex web application like the Azure or AWS consoles might have literally thousands of sources of dates formatted by a thousand different pieces of code.
Before the 12th of the month, they're all totally and utterly useless for 96% of the world unless they use ISO 8601.
BTW: I just tested this with the Azure portal by clicking through some Log Analytics related things. I got it to show me 3 different date formats, 2 of which would have been ambiguous earlier in the month, and one of which changed between two tenants. So even if you learn which parts of the UI you can trust to be correct, switching tenants will invalidate your experience.