once you choose the way to self-host you must be prepared to review changes and adopt new parameters… so as in this case domain parameter was changed in version 21-11 of collabora suite, which well documented on collabora site and within this forum as well:
be aware to adopt your reverse proxy from /loolwsd to /coolwsd for newer versions as well:
this thread with provides references which helps you to understand the integration and collect the skills to run you system for long time, and this one summarizes troubleshooting technics…