Returns the default block editor settings.

function get_default_block_editor_settings() {
	// Media settings.
	$max_upload_size = wp_max_upload_size();
	if ( ! $max_upload_size ) {
		$max_upload_size = 0;
	}

	/** This filter is documented in wp-admin/includes/media.php */
	$image_size_names = apply_filters(
		'image_size_names_choose',
		array(
			'thumbnail' => __( 'Thumbnail' ),
			'medium'    => __( 'Medium' ),
			'large'     => __( 'Large' ),
			'full'      => __( 'Full Size' ),
		)
	);

	$available_image_sizes = array();
	foreach ( $image_size_names as $image_size_slug => $image_size_name ) {
		$available_image_sizes[] = array(
			'slug' => $image_size_slug,
			'name' => $image_size_name,
		);
	}

	$default_size       = get_option( 'image_default_size', 'large' );
	$image_default_size = in_array( $default_size, array_keys( $image_size_names ), true ) ? $default_size : 'large';

	$image_dimensions = array();
	$all_sizes        = wp_get_registered_image_subsizes();
	foreach ( $available_image_sizes as $size ) {
		$key = $size['slug'];
		if ( isset( $all_sizes[ $key ] ) ) {
			$image_dimensions[ $key ] = $all_sizes[ $key ];
		}
	}

	// These styles are used if the "no theme styles" options is triggered or on
	// themes without their own editor styles.
	$default_editor_styles_file = ABSPATH . WPINC . '/css/dist/block-editor/default-editor-styles.css';

	static $default_editor_styles_file_contents = false;
	if ( ! $default_editor_styles_file_contents && file_exists( $default_editor_styles_file ) ) {
		$default_editor_styles_file_contents = file_get_contents( $default_editor_styles_file );
	}

	$default_editor_styles = array();
	if ( $default_editor_styles_file_contents ) {
		$default_editor_styles = array(
			array( 'css' => $default_editor_styles_file_contents ),
		);
	}

	$editor_settings = array(
		'alignWide'                        => get_theme_support( 'align-wide' ),
		'allowedBlockTypes'                => true,
		'allowedMimeTypes'                 => get_allowed_mime_types(),
		'defaultEditorStyles'              => $default_editor_styles,
		'blockCategories'                  => get_default_block_categories(),
		'disableCustomColors'              => get_theme_support( 'disable-custom-colors' ),
		'disableCustomFontSizes'           => get_theme_support( 'disable-custom-font-sizes' ),
		'disableCustomGradients'           => get_theme_support( 'disable-custom-gradients' ),
		'disableLayoutStyles'              => get_theme_support( 'disable-layout-styles' ),
		'enableCustomLineHeight'           => get_theme_support( 'custom-line-height' ),
		'enableCustomSpacing'              => get_theme_support( 'custom-spacing' ),
		'enableCustomUnits'                => get_theme_support( 'custom-units' ),
		'isRTL'                            => is_rtl(),
		'imageDefaultSize'                 => $image_default_size,
		'imageDimensions'                  => $image_dimensions,
		'imageEditing'                     => true,
		'imageSizes'                       => $available_image_sizes,
		'maxUploadFileSize'                => $max_upload_size,
		// The following flag is required to enable the new Gallery block format on the mobile apps in 5.9.
		'__unstableGalleryWithImageBlocks' => true,
	);

	// Theme settings.
	$color_palette = current( (array) get_theme_support( 'editor-color-palette' ) );
	if ( false !== $color_palette ) {
		$editor_settings['colors'] = $color_palette;
	}

	$font_sizes = current( (array) get_theme_support( 'editor-font-sizes' ) );
	if ( false !== $font_sizes ) {
		$editor_settings['fontSizes'] = $font_sizes;
	}

	$gradient_presets = current( (array) get_theme_support( 'editor-gradient-presets' ) );
	if ( false !== $gradient_presets ) {
		$editor_settings['gradients'] = $gradient_presets;
	}

	return $editor_settings;
}