I don’t know that. I had a look. I don’t have the “Nextcloud Office” app installed, but I don’t use ONLYOFFICE either. But maybe someone knows more. And if it’s not written anywhere, it should be documented. In free Nextcloud instances today, you will find Nextcloud Office and thus Collabora and very rarely ONLYOFFICE. This applies, for example, to Tab.Digital or Shadow Drive who both include Collabora Online for free.