First person games are shown in FulVR mode (360 environments) while third person games usually open in immersive screen mode per default since typically that makes most sense for these games.
You can change any game to FullVR mode in the vorpX ingame menu. Press [DEL] to open the menu while in the game. The option is the first one in the menu and called “Play Style”.
One very important caveat, don’t skip this: Full VR mode requires a game’s camera field of view to match the FOV of your headset or the image will look “zoomed in” or warped. vorpX can do that for many, but not for all games. If vorpX can’t do it for a game you want to try in FullVR mode, check the “Essential Hints Guide” in the vorpX help. It explains the general options you have in regard to FOV. What can be done varies from game to game.