You can use the configuration in the nextcloud folder to have a nextcloud instance with a onlyoffice configured on your homeserver. This configuration uses a nginx container and the letsencrypt-nginx-proxy-companion. Both are in the docker-compose.yml in the proxy folder.
Before using this, you need to set the variables in nextcloud/.env and nextcloud/db.env.
Nextcloud will then be available at https://nextcloud.YOUR_DOMAIN. You need to configure the onlyoffice plugin on nextcloud with theses settings:
Document Editing Service address: https://onlyoffice.YOUR_DOMAIN
Secret key (leave blank to disable): The JWT_SECRET variable in the .env file
Advanced server settings > Server address for internal requests from the Document Editing Service : https://nextcloud.YOUR_DOMAIN
You should start the nextcloud docker-compose instance before the proxy one, since the letsencrypt companion needs to detect what requests to do.