https://www.boldmethod.com/learn-to-fly/aircraft-systems/rnav-and-gps-what-is-the-difference/

So, Does RNAV Always Mean GPS?

For most general aviation pilots today, yes. But that doesn’t mean there aren’t other forms of Area Navigation. In recent history, course line computers were the most basic form of RNAV.

While GPS doesn’t automatically equal RNAV, it’s the most common system found in cockpits around the world, especially for piston aircraft.