I have a page with a date picker item (the Jet date picker) and have client-side validation off on the Submit button**.** I type in invalid value into the item - e.g. "xxx" or "32-Jan-2021" then press Submit. The items' previous valid value is submitted to the server, and when the page reloads the date input shows its previous value.
Ideally I want the invalid value submitted to the server where I can validate it with my own code (as that is what was happening prior to APEX 21.1)
This is seen by our product managers as a "show stopper" for using the Jet date picker, as it means users could save records with a different date value to the one they thought they had entered.