In our previous post How to run Collabora office for Nextcloud using docker-compose we investigated how to configure your Collabora office server using docker-compose.yml.
If you want to use multiple domains, you need to change this line in .env:
COLLABORA_DOMAIN=collabora.mydomain.com
By reading the source code I found out that COLLABORA_DOMAIN is interpreted as a regular expression. Therefore you can use a (...|...|...) syntax.
COLLABORA_DOMAIN=(nextcloud.mydomain.com|nextcloud.myseconddomain.com)
After that, restart collabora.