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?
You might try Tailscale or Wire Guard. Either can be used to create a mesh VPN that can include any device you want. Connect your devices to the VPN then you just access it like it is on your local network. Of the two I use Tailscale. Dead simple to setup on pretty much any device.
I looked into Nextcloud, but that requires paying for a domain
Depending on what installation method you choose to go with, you don’t need a domain. It’s just very much helpful to have one. Especially if you decide to have it public facing. Plus domains are cheap. A bigger issue for us self hosters is dealing with dynamic IPs. Most of the time you can buy a static IP from your ISP, but if that is not an option, most domain providers provide a way to deal with variable IP addresses.
And yes, Tailscale does ignore dynamic IP addresses. I think Wire Guard does as well as Tailscale is built on Wire Guard.