The information given here in the German Contao Wiki can lead to problems. If you want to cleanly switch back to the old ER2 in Contao, you need to follow these steps. But before doing so, you should note down all the extensions that you still need after switching back and you should make sure that these extensions are available in the ER2 and still compatible with your Contao version.
- remove all modules and assets from installed extensions (see below)
- go to System » Settings » Inactive extensions, check [!composer] and uncheck [repository]
- reinstall all needed extensions via the extension repository
- once you are sure that everything is working as expected, you can delete the folder
/composer
and/system/modules/!composer