Comment by wlesieutre

Try Settings -> Apple Intelligence & Siri -> Talk and Type to Siri

You can individually turn off 1) voice activation phrases, 2) press and hold side button, and 3) double tap bottom edge to type

For the flashlight, I assume you're talking about on the lock screen. You can customize the lock screen and remove that button entirely. If he has a newer iPhone, flashlight is probably a good use for the "Action Button" on the left, if he doesn't want to use that for toggling ringer/vibrate.