Introduces a new craft\events\BulkOpEvent::defer() method, which can be used in place of Event::on() when you want to track whether an event occurs during a bulk operation, and handle it after the bulk operation is complete.

use craft\elements\Entry;
use craft\events\BulkOpEvent;
use craft\helpers\Db;

BulkOpEvent::defer(
    Entry::class,
    Entry::EVENT_AFTER_SAVE,
    function (BulkOpEvent $event) {
        // Fetch all the entries that were affected
        $entries = Entry::find()->inBulkOp($event->key)->status(null);
        foreach (Db::each($entries) as $entry) {
            // ...
        }
    },
);

The event handler is passed the same BulkOpEvent object you’d get if you were listening to craft\services\Elements::EVENT_AFTER_BULK_OP. (The event may have occurred on a previous request, so there’s no way to keep track of the specific event objects that were fired.)