[rendaw]

And what format does work for future dates?

Or do you mean that ISO 8601 doesn't work but RFC 3339 does work or some other updated ISO/RFC format?

[mattmanser]

I'm not dealing with it anymore, I was when I worked in a couple of restaurant focused SaSSes.

Someone else has mentioned RFC 9557.

So you might be able to deal with it with 8601 for past dates and 9557 for future.