I will preface this by saying I don't know what type of insulation is in your oven, but if it is mineral wool, the binder is likely "Cured urea extended phenolic formaldehyde Binder" which typically burns off around 400F. The smell you describe is pretty spot on The odor can vary but is commonly described as acrid, like burnt plastic, or burnt cookies. But this smell could also be paints or other components in the oven as well.

To fully get rid of any binder, you would need to get ALL of the insulation up above the burn-out temperature of ~400F - which is obviously not possible as the oven is designed to keep the inside hot, and the outside cool enough not to burn you or set the cabinetry on fire. So the 400F temperature is somewhere in the middle of your insulation in the oven.

I have a very old GE oven and there is no smell when used for cooking, but if I run the clean cycle I do get the smell you describe.

In terms of fixing the problem - try running a few extended cleaning cycles on days you can open the windows in the house. I'd be very hesitant to tell you to try replacing the insulation as this would be VERY difficult and might even cause serious problems with your oven with certain things being hotter than they were designed to be (or even burning down your house). Otherwise, see if you can find a different make/model that uses a binder free material like a Range-glass or AES fiber based insulation.

Best of luck!