I think is true that the idea of ultraprocessed food is not totally well defined, but I think there are some clues that help to at least identify the most important or more ultraprocessed ones. I think one tip is: industrial manufactured ingredients that can’t be find in a regular home would potentially fall in the ultraprocessed category, so from your list:

rolled oats spun in a blender, instant oatmeal: is processed not ultraprocessed, unless the instant oatmeal it comes with ultraprocessed ingredients.

Cookies made from unprocessed ingredients, put them in a bag and sell them on a shelf: processed. The problem here is a lot of cookies that say that they use unprocessed ingredients is just not true, but if we are talking about home made cookies with basic unprocessed ingredients they would fall as just processed.

*Raw Milk: unprocessed Fresh, pasteurized milk : “minimally processed”

Brown Sugar: unprocessed white sugar: processed

white sugar and pasteurized milk mixed together: processed

Freeze that mixture? Ultra processed.* Not true, the fact of freezing doesn’t make it ultraprocessed.

I think the corporations are also trying to make this distinction more confusing to make the idea of ultraprocessed food les guilty, because if everything it may be ultraprocessed then none it is.