WordPress at a glance
function is not described

_wp_render_title_tag() WP 4.1.0

Displays title tag with content.

No Hooks.

Return

Null. Nothing.

Usage

_wp_render_title_tag();

Changelog

Since 4.1.0 Introduced.
Since 4.4.0 Improved title output replaced wp_title().

Code of _wp_render_title_tag() WP 5.5.1

<?php
function _wp_render_title_tag() {
	if ( ! current_theme_supports( 'title-tag' ) ) {
		return;
	}

	echo '<title>' . wp_get_document_title() . '</title>' . "\n";
}