Wordpress: Remove access to and hide theme editor

functions.php

<?php

/**
 * This comes in handy in cases where you can't set `DISALLOW_FILE_MODS` to `true`
 */

/**
 * Remove access to page for all users
 */
add_action('current_screen', function () {
    $restricted_screens = [
        'theme-editor',
    ];

    $current_screen_id = get_current_screen()->id;

    foreach ($restricted_screens as $restricted_screen) {
        if ($restricted_screen === $current_screen_id) {
            wp_die('You are not allowed to access this page.');
        }

    }
});

/**
 * Remove page from menu
 */
add_action('admin_menu', function () {
    remove_submenu_page('themes.php', 'theme-editor.php');
}, 999);