So I have a TrueNAS server set up at home, and it would be cool to have access to it at all times. I currently have Syncthing set up to access and back up my most essential files on my phone and laptop, but it would be nice to be able to access all the … legally obtained files I have stored there wherever I go. I looked into Nextcloud, but that requires paying for a domain. So are there any other options for this?
If you have a public IP and can forward ports, exposing SSH (with key-based login) is quite safe. You can browse the server storage and copy files to/from your phone.
If you can’t open ports you will need something that punches out of NAT and intermediates a connection to your phone. Simplest way is to use a service like Tailscale, you install and start it on both the server and your phone and they will see each other from wherever they are.