See the following Article to Install and Configure NextCloud and OnlyOffice Document Server on the same Linux Ubuntu server box, and integrate their document editing and cloud storage:

Install OnlyOffice Docs with Nextcloud on the same Ubuntu Server

The above referenced article containing the detailed installation and configuration instructions appears on InstallConfig.com.  Following is the preface summary:  

This Article applies to installing OnlyOffice docs on Ubuntu 22.04 LTS along side of NextCloud 27.0.0 with NextCloud being served via Apache2 webserver with SSL on port 443 and OnlyOffice being hosted from Nginx webserver on non-standard port 81, plus Apache2 being configured to proxy the OnlyOffice app from port 81 on Nginx to port 80 on Apache2 (and eventually port 443 on Apache2). Both the NextCloud Apache Virtual Host and the OnlyOffice Apache Virtual Host configurations will each have letsencrypt SSL certificates for their respective domains or subdomains, thus generating a separate Apache virtual host SSL.conf file for each subdomain which shall each be served by Apache on TCP Port 443. Nginx merely hosts and serves the OnlyOffice application (the OnlyOffice app) via TCP port 81 and does not need to operate with encryption and decryption via SSL certificates for the following reasons. With the Apache virtual host accessing the Nginx-hosted OnlyOffice App on localhost at port 81 and “proxying” OnlyOffice to the internet through Apache on port 443 with SSL certificate configured on the Apache virtual host ssl.conf configured for the separate OnlyOffice domain (or subdomain), there is no need to obtain an SSL certificate to bind on Nginx.

This article assumes that the apache2 webserver, php 8.1, MySQL, and NextCloud are properly installed, configured and enabled.