That isn’t how that works. Mounted ones ARE OTR’s. You need a small counter MW that you put onto a MW shelf. There is 1 mounted GE one that still swallows up your counter space except for maybe enough height for a cuttng board under it. Not an improvement in just sitting it directly on the counter.

ge spacemaker . avail in stainless bl or wh model PEM 31SFSS/ hanging kit avail sharp has a smaller 0.7 cu ft w hanging kit I believe.

GE Profile 24 Inch 1.1 cu. ft. Capacity Countertop Microwave in White · More Info

Sharp makes an 1100W Over-the-Counter (OTC) model (R-1214) that I have used since ca. 2008. It can be mounted in a corner or under a straight section of cabinets. Look at their website and follow the various links for ideas and installation requirements. If your wall is torn apart then additional mount strengthening is possible, but not required. If you want good integration with cabinets, then planning ahead is needed so that the cabinet depths match.

Note that mounting and de-mounting the unit is difficult but possible for one person; two are recommended.

The back of the unit is mounted to a supplied fixture plate attached to the wall.

Caution: The front of the unit is held up by machine screws that go through the cabinet base and into the microwave oven assembly. Do not use these screws to pull up the unit; the threads may strip. Instead push the unit up flush to the cabinet (with blocking, books, cabinet jack, whatever) and tighten down the screws. Don't be afraid to use large washers to spread the force on the cabinet base. Obviously, the cabinet itself has to be well secured.

GE PEM31 Profile 1.1 Cu. Ft. Countertop Microwave Oven

We have a Miele speed oven installed below counter. It's our only microwave. I don't like using a below the counter microwave. If undercounter were my only option, I'd do a microwave drawer.