That is what is referred to as a POM (previous owner modification) as opposed to a POS, which is self explanatory. It looks like a car floormat screwed into the the deck as some sort of anti-skid device to reduce abrasion of the deck. Maybe an anchor point for an inverted dinghy. Are those rubber o-rings under the stainless cover, or cables? Maybe a place to locate a battery for charging off of portable solar panels. The only thing recognizable is the straight screw driver. It’s fun guessing, but I really haven’t a clue. Maybe look under the mat? Take a secondary image from a few more feet back?