Datepicker no longer working since WordPress 5.3

After a site hack we had to restore our site back from 1 month ago.

Taking some slightly panicky and hasty security action we also updated to WordPress 5.3.2 from 4.8.

Since the update the date picker has ceased working. Not wanting to start again pre wordpress update and given that we no longer have contact with the developer that built our site Id hoped someone could provide a novice on where I might look.

We’re running ACF Pro v5.5.5 . This plugin is part of a small hidden group of ‘must use’ plugins that dont appear to have the usual update button or update notification that wordpress usually allows plugins to display. So we are unable to update this plugin in the usual way.

Could someone possibly offer a relative novice some help and advice on where or how I can go about fixing this small but crucial feature?

Many Thanks