Depending on a game, either of the two:
- Right joystick with continuous activation or release (latter being less reliable)
- Right trackpad menu in an action layer, sometimes through a chord
For example, I can have the right trackpad behave as mouse most of the time, but switch to a virtual menu on click, each item also being activated on click. Some of these items can be bound to weapons, but if that's not an option, like there's being more weapons than I can comfortably fit onto my virtual menu alongside all the other stuff I may want to see there, I could hold L5 to turn the trackpad into a different virtual menu, all dedicated to weapons. I often use gyro on right trackpad touch, so I'm okay with giving mouse input on it for a few moments when I'm switching a weapon.