I believe polenta, corn meal, grits, and corn flour are not. But how about tortilla corn chips you buy at the supermarket? This is what I am looking for!
I have a link to a quora question that I believe is wrong in that it says most corn products in the United States are but I read just the opposite on other sources.
Still searching, this is a tough question. Here is the link which gives various opinions. https://www.quora.com/Why-isn-t-nixtamalization-a-standard-process-for-corn-production-outside-of-Central-or-South-America-European-settlers-seem-to-have-just-ignored-and-eliminated-the-process
P.S. After posting this I discovered a corn chip made with mesa flour! It's called Calidad. It's the only one so I assume the quora answer is incorrect. If it does not list as mesa flour probably the corn meal is not nixtamalized.