Cant seem to find Collabora setup for Built in code server with Apache reverse proxy

Can anyone point me to a setup for the following.

Snap Nextcloud with Collabora built in code server one machine.
Apache reverse proxy on on other machine with https>http>Nextcloud IP.

Onlyoffice setup and works ok. Collabora setup and works ok without the reverse proxy and just accessing NC via the machine IP. But when NC is accessed via the apache reverse proxy using the domain name, where Collobra should be it is just a white page. No errors showing in NC logs.

I found the instructions for setting up Collobra docker and reverse proxy but not for the built in code version.

I have the same problem. Symptoms exactly like NextCloud HTTPS (via reverse proxy) and built-in Collabora not working except my Nextcloud is not in a Docker container. Did you find how to fix it?