Find another rule
drupal/core 11.2

EntityFormModeEmptyDescriptionToNullRector

Replace empty-string description with NULL in EntityFormMode::create() calls (deprecated in drupal:11.2.0).

 EntityFormMode::create([
   'id' => 'user.test',
   'label' => 'Test',
-  'description' => '',
+  'description' => NULL,
   'targetEntityType' => 'user',
 ]);

Configure your rector.php:

<?php

use DrupalRector\Drupal11\Rector\Deprecation\EntityFormModeEmptyDescriptionToNullRector;
use Rector\Config\RectorConfig;

return RectorConfig::configure()
    ->withRules([
        EntityFormModeEmptyDescriptionToNullRector::class,
    ]);

Other rules in the drupal/core 11.2 set