The WS Form Light plugin is compatible with ClassicPress, because it also fully functions without the block editor. Yet, it does check if the block editor is available.
This check is only called by clicking a Post or Page title in the Admin, but if the “Blocks Compatibility” dropdown in Settings > General is set to “Off” (value 0) a fatal error will be triggerd in /wp-admin/includes/class-wp-screen.php on line 438.
This line calls the WP_Compat class, which does not seems to be loaded if the Blocks Compatibility is off. Setting that to either “On” or “Troubleshooting” does not trigger the fatal error.
