“Not at all” is how to use it–TrueNAS itself is perfectly capable of handling this. Here’s a walkthrough of how to do it on CORE; the UI in SCALE (you haven’t said which version of TrueNAS you’re using) is likely a little different. When you get to the cert itself, you’d want to include the IP address in “Subject Alternative Names”:
I’d say pretty much nobody needs to go through this for a home storage server. TrueNAS creates a default cert on installation, and that’s adequate to secure communications. Sure, your browser will give a cert warning, but you can bypass those. And if you want a cert that will work without warnings, the way to go is to get one from a trusted CA, not to mess around with self-signed certs. But if you nonetheless want to use a different self-signed cert, the link above gives instructions for making one.