Datepicker m/d/Y

Have you adjusted the settings here to suit your needs? : on Dashboard – Settings – General – “Date Format”

if that does not work – try in your child-theme functions.php:

function new_date_format() {
  $date_format = "m/d/y";
return $date_format;
}
add_filter('avf_datepicker_dateformat', 'new_date_format');

and if you like to influence the placeholder text:

function new_date_placeholder() {
  $placeholder = "TT / MM / JJ";
return $placeholder;
}
add_filter('avf_datepicker_date_placeholder', 'new_date_placeholder');

PS: for Formatstring see: https://wordpress.org/documentation/article/customize-date-and-time-format/

no chance to get it with quick css.

there are possibilities to insert that snippets in parent theme functions.php – but on every update you will loose those changings.
See enfold functions.php file on line 1011ff – there is a comment :

/**
 *  register custom functions that are not related to the framework but necessary for the theme to run
 */

So if you want to get by without a child theme and don’t want to incorporate the changes every time you update, there are plugins that can embed code snippets. f.e. https://en-gb.wordpress.org/plugins/code-snippets/

I always install a child theme, so I can’t help you with that.