_add_themes_utility_last() │ WP 3.0.0

Adds the 'Theme File Editor' menu item to the bottom of the Appearance (non-block themes) or Tools (block themes) menu.

Internal function — this function is designed to be used by the kernel itself. It is not recommended to use this function in your code.

No Hooks.

Returns

null. Nothing (null).

Usage

_add_themes_utility_last();

Changelog

Since 3.0.0 Introduced.
Since 5.9.0 Renamed 'Theme Editor' to 'Theme File Editor'. Relocates to Tools for block themes.

_add_themes_utility_last() code WP 6.9.1

wp-admin/menu.php 
function _add_themes_utility_last() {
	add_submenu_page(
		wp_is_block_theme() ? 'tools.php' : 'themes.php',
		__( 'Theme File Editor' ),
		__( 'Theme File Editor' ),
		'edit_themes',
		'theme-editor.php'
	);
}