How can I fire the SFAR-M GL granades?
I unlocked the SFAR-M GL rifle and I can choose between different grenade types in the customize menu.
When equipped with this rifle, how can I use this grenade launcher?
Depends on what platform you're on. If you're on console (PS4/5, Xbox), hold down(↓) on your D-pad. If you're on PC, simply hit X on your keyboard.