May 27, 2020
Disable the default from WordPress version 5.4 that forces fullscreen mode as the default view in Posts, and Pages.
function jba_disable_editor_fullscreen_by_default() {
$script = "window.onload = function() { const 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', $script );
}
add_action( 'enqueue_block_editor_assets', 'jba_disable_editor_fullscreen_by_default' );