Hi Vijayakumar Gade,
I think The validation for default datepicker widget can't be overridden, so you might need to implement this function with text fields and regular expression.
else you can try to handle the invalid date calculation in the microflow and set the date to empty and refresh the object. I guess you can use onchange microflow in react-datetime picker.
In your microflow check first if the date is empty and then check if the date is invalid , if yes, set the date attribute to empty and if valid , leave it as it is.
If the field becomes read-only even for valid date just I my case I use the default format and it works for me...
Hope it helps.