Iberia operated by Level

I booked a cheapo flight from SFO-BCN through American Airlines. It said the flight was operated by Iberia. After trying and failing to select a meal on the Iberia website, I just realized today that the flight is actually operated by Level and doesn’t include meals at all. I can cope with that, but now I’m worried about how strict they will be with carry on and personal item size/weight since it’s a low cost carrier.

Has anyone flown this route recently, or with Level in general? Can you speak to how strict they are? Like are they going to give me a hard time if my personal item backpack is 3 inches taller than their max?