Collabora Online bot in port 443

Hello,
because the port 443 is in use by an another application I have to do my setup of nextcloud on

https://office…mydomain.de:8443/nextcloud

The server is an ubuntu 18.04. With nginx mariadb fail2ban, redit, php7.2

I am not able to get collaborators online running on this setup. Have anyone an idea how to solve this, or is it possible at all to run this with a different port in the url.

Thanks a lot for any advices…