Just as info:
in certain forms, I'm passing an extra parameter (for example seminar data) directly in the url of a registration button:
<a href="index.php?option=com_breezingforms&view=form&Itemid=492&seminar=Zertifikation%20Zauberpinsel-%20PädagogIn%20IKE"
this code is taken with php in the field:
<?php $tmp = JFactory::getApplication()->input->get->get('seminar','','STR');
if (!empty($tmp)) { return $tmp; } ?>
After upgrading to Joomla! 4, the form in the front end is not found anymore, respectively the routing doesn't work anymore. The J!4-routing tries to do something with extra parameter and therefore the form is not found anymore....
attachment 1: the url in J! 3
attachment 2: the seminar field in J!3
attachment 3: the url with J! 4 (locally)
the result is 404 - page not found.