I have a stainless steel backguard behind my gas range that was purchased and installed for approximately $100. It extends several inches beneath the range.

most backspalsh materials should be able to withstand heat. Perhaps a wood or metal base will help raised the toaster oven's heat away from the backsplash.

I have a large air fryer that generates a lot of heat too. I put it on a large thick cutting board when in use and pull it away from the backsplash. Easy!

Thanks for the suggestions. I saw some clear tempered glass cutting boards that withstand heat up to 365 degrees. That should do the job.

Or

That won’t work either. A non combustible material top of a combustible one doesn’t make the combustible one into a non combustible. It just transfers the heat. It doesn’t block it. You place that on a counter, and place a crockpot on top of it, you’re just transferring heat to the counter.

>>>"What do you do to protect the countertop, backsplash and underside of the wall cabinet from the heat?""<<

Read the owner's guide/manual and observe the directions for spacing. The exterior casing can get hot enough to burn bare skin but that heat falls off pretty radically with a modicum of spacing. You protect countertop and walls by not removing the feet from the bottom or the stand-offs from the back, (Would it have even occurred to you to do that?)

The manual/user guide will advise keeping several of inches of space between the oven's top and the bottom of the cabinets above it. So don't shoehorn the oven into a tight shelf space and try to run it there. After all, they are called countertop ovens because they are meant to be used on countertops with a bit of space around them.

Now, FWIW regarding glass cutting boards --- I've used a glass cutting board under my toasters and toaster ovens for years. Never singed or discolored formica counterptops nor the wooden countertop that my current countertop oven currently sits on. I use the glass because it is easier to clean than the wood not because I'm fearful of igniting or melting the countertops.

In the interests of science --- and maybe for another appliance-geek merit badge :>) --- I cranked my countetop oven to 450°F for an hour with a temperature probe under the center of the glass board under my largish countertop oven. Temperature rise under the center of the glass was from room temperature to about 100°F. That was the extent of the heat transfer to a combustible (wood) surface. Hardly a combustion risk, eh?

For 14 years, I had my large toaster oven sitting under my cherry wood cabinets, against my sheet rocked backsplash (never got around to installing a proper backsplash), and right next to the cherry wood oven cabinet. Never had a problem with excessive heat or damage on any surface. Granite was fine, as well. I did not pull it out to use.

Should I be more careful in my new kitchen? I will have a hard marble or quartzite type countertop, a tile backsplash, and painted cabinets.