A simple Wordpress-Plugin to render "Open All" & "Close All" Buttons to Admin Pages with ACF Flexible Content
Go to releases and download the most recent version.
In WP, go to Plugins > Add new and click the upload button.
Once activated, in WP-Admin, on Pages, Posts and everywhere, where ACFs Flexible Content takes place, two buttons will be rendered: One to open all panels and one to close all of them.