To add a category to all events using The Events Calendar in WordPress

Add category to all events.php

// Add category to all events
function add_category_to_all_events() {
    // Get all events
    $events = get_posts(array(
        'post_type'      => 'tribe_events',
        'posts_per_page' => -1, // Get all events
    ));

    // Check if events are found
    if ($events) {
        foreach ($events as $event) {
            // Get current event categories
            $categories = wp_get_post_terms($event->ID, 'tribe_events_cat', array('fields' => 'ids'));

            // Add your category ID to the event's categories (replace 'your_category_id' with the actual category ID)
            $categories[] = 'your_category_id';

            // Update the event with the new categories
            wp_set_post_terms($event->ID, $categories, 'tribe_events_cat');
        }
    }
}

// Hook the function to run on activation (you can remove this line after running it once)
add_action('init', 'add_category_to_all_events');