Old config not usable

Problem/Motivation

Hello the menu we build with the drupal 8 version of the module does not work anymore, after the update to drupal 9.

Steps to reproduce

We updated the module from Drupal 8 Version to Drupal 9

Proposed resolution

Find a way to use the same menu we build with drupal 8 version

I used the readme to build this menu again with the D9 Version but i can not get it to work.

Here my steps:
0. create a menu named 'mmenu' [ /admin/structure/menu/manage/mmenu ]
1. build menu--mmenu.html.twig
2. in page.html.twig

3. put this in a custom block :

Menü

i know that these steps are not the same as in the readme but i have to do this way because

5. use javascript to trigger the menu
6. nothing happens