The square holes at the top of the insert are where we install the electronics. They are hand holes and not vents, and therefore can be covered. It’s normal to trim in or frame over these square openings. They are not meant to be visible and will not need to be seen.
Warning: In most cases almost all maintenance can be done from within the fireplace opening itself. However, under some rare occasions you may need to access the square holes for maintenance or repairs. Since forever is a long time, and this is installed in your wall, you may want to consider that the trim pieces at the top that cover the holes to be somehow removable, just in case you need to access these at some point in the future, even though unlikely for many years.