Problem

In another tutorial I wrote that automatic updates are the easiest method to update themes in WordPress. Add the following code and WordPress will update each theme once a new version is available. It uses the auto_update_theme filter.

// Enable automatic updates for all themes
add_filter('auto_update_theme', '__return_true');

The main risk of this method is that problems may happen if the active theme is updated automatically, but the new version is incompatible with plugins, custom CSS rules, etc.

Exception

If you trust enough in your theme provider and conflicts are unlikely to occur after an update, a good decision would be to turn on automatic updates for the active theme and other installed themes of your choice.

Add the following code and WordPress will enable automatic updates for themes whose slug is listed in the $allowed array.

/*
 * Enables automatic updates for specific themes.
 */
function ns_auto_update_specific_themes($update, $theme){

    $allowed = array('theme-1', 'theme-2', 'theme-3');
    return in_array($theme->slug, $allowed) ? true : $update;
}
add_filter('auto_update_theme', 'ns_auto_update_specific_themes', 10, 2);

User interface

WordPress 5.5 added a user interface to make the procedure described above easier.

Step 1: Navigate to Appearance and click on a theme.

Step 2: Click the link to enable or disable automatic updates.

Tip

A WordPress website only requires one theme, the active theme. Delete other installed themes whenever possible. These themes are a waste of resources, and their vulnerabilities are open doors for attackers.

Source code

The source code developed in this tutorial is available here.