Menu does not work after Update from 3.3.6 to 4.5.6 on Joomla 4.4.10

Hi,
i tried 3 times the update from the Menu and i get always the same result.
I updated with the pkg_jux_megamenu.J4.J5.zip file.

All i could find out is that the css might not load correctly if i compare the code with the old one (the productive site is on rats-ms.de). Changing the Layout changes not the rendered html, the custom-213.css (213 is indeed the menu module) has just empty attribute values).

Any help is appreciated, thanks in advance!