i guess we are at the age where we need to replace microwaves- in my 2006 Pleasure-Way the microwave is on top of an armoire- PW used 4 screws up through the cabinetry into the steel base of the microwave.
The microwave was 700watts and the space available is quite limited...
I bought one which would fit and of 700 watts, $90 Amazon, and mounted same way making a template for the mounting screw location and then moving that around on teh bottom of the new MW until I have all 4 screw locations into good steel.
Drilled pilot holes and it worked out fine.
Comfee CMO-C20M1WB
What's funny is that we almost never use it - we store our plates and dishes inside the microwave.
I know some other owners on my FB group have instead installed MW/Convection/ air fryers- but I didn't have room- if you have room it may allow for some of those options which you could look into.
Pay attention to any venting requirements.
as far as removing the fridge some youtube videos will give a rough idea of what it'll take.