Leave a cup of cloudy ammonia in the oven overnight. It loosens the dirt. I did a whole blog post on the best way to clean your oven. You might like to read it. https://www.livingareallife.com/posts/how-to-clean-an-oven
Vinegar, water and baking soda is what I use. I sprinkle the baking soda on the area and spray with a mix of half vinegar and water. You can use a spray of vinegar without the water too but first use the diluted part first. Allow it to stay for about an hour or so spraying the vinegar again in-between. Then wipe and if there are stubborn hard pieces repeat the process. If you need to remove pieces carefully use a Teflon scrapper than is not too hard but you should easily be able to remove the pieces. Just a note: I use a Teflon liner at my bottom which really saves for a lot of these messes. You can easily remove it and clean with out any difficulty. I do have a self cleaning oven but prefer to not use it regularly.
FYI: And for oven grills...Place paper towels in a large garbage bag lined with paper towels in between grills. Pour 1 cup Household ammonia over paper towels, seal bag and allow to set overnight in garage or well vented area. They wipe up really clean. Good Luck. M.j.