I noticed "donut" was missing from the dictionaries (with the note: level 2 variant [v]), but "donuts" is present (with the note: found in "hacker" list [sl]).

Donut has a "should include" score of four stars (****) based on the Google Books Ngam dataset.

Anecdotally, "donut" is an extremely common variant in American English, perhaps more common than "doughnut".