Source

File: wp-admin/includes/class-wp-posts-list-table.php

protected function formats_dropdown( $post_type ) {
		/**
		 * Filters whether to remove the 'Formats' drop-down from the post list table.
		 *
		 * @since 5.2.0
		 * @since 5.5.0 The `$post_type` parameter was added.
		 *
		 * @param bool   $disable   Whether to disable the drop-down. Default false.
		 * @param string $post_type Post type slug.
		 */
		if ( apply_filters( 'disable_formats_dropdown', false, $post_type ) ) {
			return;
		}

		// Return if the post type doesn't have post formats or if we're in the Trash.
		if ( ! is_object_in_taxonomy( $post_type, 'post_format' ) || $this->is_trash ) {
			return;
		}

		// Make sure the dropdown shows only formats with a post count greater than 0.
		$used_post_formats = get_terms(
			array(
				'taxonomy'   => 'post_format',
				'hide_empty' => true,
			)
		);

		// Return if there are no posts using formats.
		if ( ! $used_post_formats ) {
			return;
		}

		$displayed_post_format = isset( $_GET['post_format'] ) ? $_GET['post_format'] : '';
		?>
		<label for="filter-by-format" class="screen-reader-text"><?php _e( 'Filter by post format' ); ?></label>
		<select name="post_format" id="filter-by-format">
			<option<?php selected( $displayed_post_format, '' ); ?> value=""><?php _e( 'All formats' ); ?></option>
			<?php
			foreach ( $used_post_formats as $used_post_format ) {
				// Post format slug.
				$slug = str_replace( 'post-format-', '', $used_post_format->slug );
				// Pretty, translated version of the post format slug.
				$pretty_name = get_post_format_string( $slug );
				// Skip the standard post format.
				if ( 'standard' === $slug ) {
					continue;
				}
				?>
				<option<?php selected( $displayed_post_format, $slug ); ?> value="<?php echo esc_attr( $slug ); ?>"><?php echo esc_html( $pretty_name ); ?></option>
				<?php
			}
			?>
		</select>
		<?php
	}