Fix the missing or blurred hamburger icon in the navigation menu after upgrading Oracle APEX 5.X to a higher version

Introduction After upgrading my APEX app from 5.1 to 21.1 I struggled with the lost hamburger icon in the navigation menu, like this: A quick fix can be tricky. If we inspect this corrupted element (Chrome F12), we can find: <span class="t-Icon fa-b...