The best are that have a settings page where they try to give an example. But use a day-of-month =< 12. Like your example. It couldn't have hurt to use and example of "22/05/2020"; then it is still infuriating, but clear.
Assuming you're addressing OP with this part, I think that was their point.
When an application presents you with "04/05/2020", you have no way of knowing whether it means crazy American dates or normal-people dates.
In just about every professional setting I've been in (in the US), Americans are just as confused as everyone else. We deal with people and documents/data from the entire world too. We look for clues elsewhere, such as other dates from the same source that have any number greater than 12, etc. There are very few documents these days where you be 100% confident without some other confirmation.
Of course, the Romans didn't use 'BCE' at that time. They referred to years by the consuls who held office that year.