date picker not working

The date picker isn’t working for me to select a estimated completion date. I also can’t determine the format of the date to enter my own date manually (what is the format?)

This is the error that firefox provides. I have also tried Edge:

https://www.----.com/wp-content/plugins/wp-socializer/admin//js tinymce.js:10:21
MouseEvent.mozPressure is deprecated. Use PointerEvent.pressure instead. 2 tinymce.min.js:2:8856
This site appears to use a scroll-linked positioning effect. This may not work well with asynchronous panning; see https://developer.mozilla.org/docs/Mozilla/Performance/ScrollLinkedEffects for further details and to join the discussion on related tools and features! post.php
Uncaught TypeError: $(...).zIndex is not a function
    _showDatepicker https://www.----.com/wp-content/plugins/bug-library/js/ui.datepicker.js?ver=5.6.1:685
    _attachments https://www.----.com/wp-content/plugins/bug-library/js/ui.datepicker.js?ver=5.6.1:233
    jQuery 2
ui.datepicker.js:685:31

?