On my nextcloud 18.0.8 I tried to activate CollaboraOnline, and needed a server.
From the https://<hostname>/nextcloud/index.php/settings/admin/richdocuments
I clicked on the Install it from the app store and I landed in https://<hostname>/nextcloud/index.php/settings/apps/app-bundles/richdocumentscode but I could not find where I should click:
Collabora online built on server is not available for nc 18. You need first upgrade your nc to the latest version (19.0.2).
Don’t install only office built in server, there is a major bug