The toaster fits neatly beneath the upper cupboard, right beside the bread. That is a storage observation. Heat rises out of the slots during use, and the correct operating position needs a separate check.
There is no useful universal cupboard gap
Find the model number and its instructions. A pop-up toaster and a countertop toaster oven are different appliances, with different heat patterns and placement requirements. Do not borrow a clearance from another brand or infer permission because your cabinet has not discoloured yet.
Breville: BTA820XL, BTA830XL and BTA840XL toaster instructions calls for a stable heat-resistant surface and warns about combustible materials near or above the covered toaster models. Follow the instructions for your appliance, including any restrictions on enclosed spaces. Cabinet doors, curtains, paper towels and a bread bag all belong in the placement check.
Cool appliance
Move it to a location permitted by its instructions.
Operating position
Keep required clearances and the cord clear of heat and water.
After use
Unplug as instructed and let the appliance cool before storage.
Moving it forward is not automatically enough
Check whether moving the toaster puts it near the counter edge, sink splash area or a crossing point where a sleeve can catch the cord. Keep every foot supported. A cramped appliance garage with its door open may still leave the toaster surrounded by surfaces its instructions prohibit.
Do not improvise a heat shield as a substitute for the required location. A sheet of metal can become hot itself and does not change the manufacturer's approval. If the only possible position is unsuitable, choose a different kitchen arrangement rather than making breakfast depend on remembering an exception.
Make routine care easy enough to happen
Leave a way to remove and clean the crumb tray after the appliance has cooled, following the manual. Do not reach into the slots with utensils or try to remove stuck food while it is connected. A storage location that makes unplugging or cleaning difficult is likely to be inconvenient every week.
When planning new cabinetry, reserve an operating patch of counter for hot appliances rather than filling every gap with storage. A coffee-maker appliance garage has a related but different moisture problem. Both need the actual appliance instructions before the cabinet is designed around them.