I don't understand why your upper cabinets are not 12" deep.

I have no darn idea. Seems as if every project I attempt, there's a hurdle, but I'm motivated to keep pushing.

Here's a photo of the kitchen reno. If anyone can give insight, that would be a blessing.

So this is an OTR microwave that will also exhaust your cooktop? If so, then it is supposed to stick out. Maybe I am not understanding your issue. Can you explain further.

This is a side profile of my cabinets. In a normal case, the microwave brackets are placed on the back wall and the microwave fits snug. Because of my cabinet depth, there is about a 3.5 inch gap in the back. Manufactorers provide "bump out kits" which are basically brackets with a 2in lip to help support the microwave despite the possible 1 inch gap. That scenario = 1 inch gap. My scenario = 3.5 inch gap. There aren't any "bump out kits" for my gap. I understand that it is a must that the microwave sticks out for the vents on the top. What can I do about the back?

It has to stick out. Any local metal fabricator can make you an L shaped piece of stainless to mount over the blocking.

How about getting an undercabinet hood instead? IDK if you would have the same issue.

Well, I have a $500 microwave that I'd really like to use.

Then spend the $200-$300 to block out the rear to accept the bracket and have a custom piece of stainless fabricated. OTR’s aren’t very good vents. And they are kinda unsafe to use as microwaves too. Compromise appliances rarely perform all of those multiple functions equally well. But sometimes space available dictates the compromise.

All IKEA wall cabinets are 15" depth now so this comes up often...

Thank you Hallett! And also for the headsup on the venting. I bought a house that my inspector apparently didn't do a good job inspecting.

I don't think I have ever seen an OTR microwave that is less than 30" in width

Beverly, that is the 'side' profile of the microwave to illustrate the mounting issue. The width of the microwave is 30inches.

What kind of space do you have from the top of the range/cooktop to the bottom of the cabinet? And I'm with mackdolan and live wire oak. Talk to a sheet metal fabricator.

No.,......this is the area that doesn't appear to be 30" wide to receive the OTR microwave

Ok, I understand your point. It may just be the angle of the photo with the shadow and everything. It's a tiny bit larger than 30" :) Perfect fit

I don't see the comment I added yesterday, so again...

There are vent hoods out there can exhaust into a rectangular opening, usually 3.5" x 10" or there abouts. how large is your opening?