If you want to connect with Nextcloud, you have to install the [Collabora Online](https://apps.nextcloud.com/apps/richdocuments) app in Nextcloud, and configure it with the domain of your Collabora installation.
*:warning: There are several Collabora Online apps. Be sure **not** to install the `Collabora Online - Built-in CODE server` apps, which are a lightwheigt version of this Collabora package. :warning:*