The module's settings aren't correctly passed into Mmenu on the JavaScript side. This is due to breaking changes that took place in 9.0, 9.1, and 9.2.
Update the module to comply with the changes by correcting the Mmenu configuration and options in `responsive_menu.config.js`. The current Mmenu documentation is located here.
There are also some additional options available in this version, such as high-contrast themes, that should be added to the settings form.
Active
5.0
Code
Created patch for Merge Request 21: https://git.drupalcode.org/project/responsive_menu/-/merge_requests/21