The new ingredient is something that should be readily available this time of year, as well as versatile: Zucchini/Courgettes. It looks like the last time this was a stand-alone ingredient was 2016. The last time it was part of a challenge was when Squash was the ingredient, and these were allowed.
But, I'd like the challenge to be just for Zucchini/Courgettes, and not expanded to all squash.