We tryed it again. First installing the new version of Lotus theme (1.04 -> 1.05), then uninstall the plugin Enable jQuery Migrate Helper, then refresh all, delete all cache. We also looked into the website with other browsers where no cache of this website was before.
All seems to work fine, but the navigation is broken and we do not know why.
Before, the website looked like this:
Ater, the website looked like this:
We recovered the website again and are now back to version 1.04 of the theme.
Perhaps you have an idea, why the navigation is broken after update.