Trying to place an outlet plate flat to the wall
JACK is talking about the drywall ears on the corner, which are designed to catch the edge of the drywall to hold the switch flush to the drywall.  That is because boxes are often sunk a bit into the drywall, because in new construction, boxes are installed before the drywall.  So the ability to install the box a bit &quot;deep&quot; gives the builder some tolerance to work with.
Anyway, if the box is sunk, you can take advantage of that, as JACK says.  Now first, you can try simply bending the drywall ears just right so the switch sits a little lower.   If you've already broken them off, do not leave the switch to float -- use shims to hold the switch at the right height.
Or, try other varieties of screw, such as a countersunk (aka flathead) or oval/pan head. The thread is #6-32. Don't change threadings; you will gore up the threads on the box, and then nothing will work.
Regardless, you must follow any instructions or labeling on the cover (NEC 110.3(B)).  The instructions are part of what UL approved when they approved the cover.