Steps to reproduce the issue

Try this code anywhere you can

use Joomla\CMS\Factory;

$app    = Factory::getApplication();
$model = $app->bootComponent('com_content')
                          ->getMVCFactory()
			  ->createModel('Category', 'Site', ['ignore_request' => false]); // we try to get exists model in

				$category           = $model->getCategory();

And we have an error: Call to a member function get() on null /components/com_content/src/Model/CategoryModel.php:338

If you'll add a line

$model->getState('category.id');

and then $category = $model->getCategory(); - there are no any errors.

Joomla 5.4. With Joomla 5.3 there were no such errors.