@guy123 welcome and thanks for your request 
your setup is unclear from the information you’ve mentioned:
- nextcloud snap installed on bare metal host behind nginx reverse proxy on the same host, right?
- FQDN correctly configured as per How to manage Hosts and FQDN for Nextcloud snap, right?
ergo, Nextcloud snap is running on a port other than 80 (which port is that?) → nginx reverse proxy is internet facing on ports 80 and 443 forwarding the snap and doing the SSL stuff.
its unclear how you’re installing eurooffice though… assuming its a bare metal install on that same host using *.deb or make, you’d need to configure a port other than port 80 (nginx), port 8x (Nextcloud snap) and configure a proxy host in your reverse proxy, forwarding that eurooffice port.
but those are assumptions and without details we’re just guessing.
recommend running eurooffice in a docker container on that host see Euro Office for Nextcloud with Docker that way you’re not interfering with the snap and you’ve separated the snap and eurooffice environments, each running in their own contained environment and letting nginx handle the routing and SSL
@jtr the eurooffice app from the app store is merely complaining that it can’t connect to the service that was configured in the adminsettings
→ so its not a confinement issue as the eurooffice service is not running within the snap and confinement will only effect binaries executed within the snap.
personally been running eurooffice and collabora in parallel on the snap for a while now, without any issues.
thus @guy123 should be able to run all those services on one host, provided the services are each correctly configured and the nginx proxy hosts are forwarded correctly.