Do not limit 3 categories

There is no reason to limit.
By default there should be no limit.
If a specific installation needs a limit, it can set it itself.

Configuration/TCA/Overrides/tx_events_domain_model_event.php

@@ -10,7 +10,6 @@ defined('TYPO3') or die();
         'label' => 'Categories',
         'fieldConfiguration' => [
             'minitems' => 0,
-            'maxitems' => 3,
             'multiple' => true,
         ]
     ]