I had a working Nextcloud / Collabora installation on my local server until recent update of docker image collabora/code to version 6.4.3.1 (latest). After reverting back to previous docker image 6.4.2.2 it works again.
To me it seems that something changes with latest collabora/code docker image 6.4.3.1
Found an issue on the Collabora Github which suggests that the syntax might have changes and no backslashes are required anymore in the domain name (escaping the dots). After removing the backslashes in the domain names, the latest version 6.4.3.1 works fine, no “unothrised WOPI” error anymore 