Like many self hosted solutions, Onyx is docker compose ready. The official image of Onyx can be downloaded from Docker Hub.
On the official Docker Website you can find the instructions on how to install the current Docker version.
If you have never heard about Tailscale, you will be in for a treat. It makes it easy and secure to access your server via a wireguard vpn tunnel. And it gets better: You can easily create a mesh vpn network! And even better: It’s free for personal use.
To get started using Tailscale, I recommend the YouTube Video How to get started with Tailscale in under 10 minutes by the great Alex Kretzschmar. If you’re interested in self hosting, his nickname ironicbadger should ring a bell.