The whole pattern of considering an input field being blank or having an invalid value while still focused causing an error indicator of any kind to appear is surprisingly infuriating to me.

Like it’s actively frustrating to focus a field like a phone number entry and already the field is red and says something like “must be a valid phone number”. Yes I know that! I’m trying to enter one! Stop drawing my attention to useless information!

Displaying some kind of error if I focus away and the input is invalid or blank is marginally better (and I can see how in some cases might be a better choice, even), and displaying an error “on submit” (for some definition of submit) seems utterly reasonable. But before the user even has a chance to enter a valid value is just a good way to piss them off.