You can switch to FullVR mode for every game if you want, the default is just what I think makes most sense for a game.
First person games always default to FullVR, third person games usually default to immersive screen mode since that makes more sense for third person. Many third person games are also enjoyable in FullVR though if you want to do that. May involve some old-style manual FOV tweaking though if vorpX can’t do that automatically.
For cockpit (racing) games you should check whether a game has a cockpit perspective and ideally TrackIR support (to be used with OpenTrack).