Switching Gutenberg to fullscreen mode requires setting to TRUE fullscreenMode from the core/edit-post package. To enqueue appropriate script, you use enqueue_block_editor_assets action hook. function se337302_fullscreen_editor() { $js_code = “jQuery(document).ready(function(){” . ” var isFullScreenMode = wp.data.select(‘core/edit-post’).isFeatureActive(‘fullscreenMode’);” . ” if ( !isFullScreenMode )” . ” wp.data.dispatch(‘core/edit-post’).toggleFeature(‘fullscreenMode’);” . “});”; wp_add_inline_script( ‘wp-blocks’, $js_code ); } add_action( ‘enqueue_block_editor_assets’, ‘se337302_fullscreen_editor’ );