I have nextcloud installed on a home server based on Debian 11 and working without problem,
We use them 7 users to share photos, videos and family documents.
I have installed Collabora-office and I can’t open, create or edit office files, although it seems to be correctly configured in the nextcloud configuration, where the collabora url is entered, and I even see the office symbols when I click on the cross to upload files, create folders or create files.
I have you checked in the dev tool on the browser ? You can view if you browser is trying to access your Collabora-office server.
From the look of it might be your Collabora-office server’s certificate that is not trusted by your browser.
If you try to access your Collabora-office server directly is there any warning about the certificate not being trusted ?