So basically you have docker and may be docker-compose already installed and configured, why you need this tutorial then? Just go the source of nextcloud docker and read how to:
Then just use docker compose, it has already mariaDB, even HTTP2:
and HTTPS:
https://github.com/nextcloud/docker#https---ssl-encryption
Or, better to build a Frontend e.g. with Apache and Lets encrypt:
https://www.digitalocean.com/community/tutorials/how-to-secure-apache-with-let-s-encrypt-on-ubuntu-18-04