Astra_Meta_Boxes::setup_meta_box()

		public function setup_meta_box() {

			// Get all public posts.
			$post_types = get_post_types(
				array(
					'public' => true,
				)
			);

			$post_types['fl-theme-layout'] = 'fl-theme-layout';

			$metabox_name = sprintf(
				// Translators: %s is the theme name.
				__( '%s Settings', 'astra' ),
				astra_get_theme_name()
			);

			// Enable for all posts.
			foreach ( $post_types as $type ) {

				if ( 'attachment' !== $type ) {
					add_meta_box(
						'astra_settings_meta_box',              // Id.
						$metabox_name,                          // Title.
						array( $this, 'markup_meta_box' ),      // Callback.
						$type,                                  // Post_type.
						'side',                                 // Context.
						'default'                               // Priority.
					);
				}
			}
		}