The short answer
Yes — plain air-popped popcorn is a fun, safe treat.
Why
Air-popped popcorn with nothing on it is a safe, light treat, and budgies enjoy pecking it. Never salted, buttered or microwave popcorn — too salty and fatty. A few un-popped kernels also make a good foraging treat.
How to feed it
Offer a piece or two of plain air-popped popcorn, or a few dry kernels to crack.
How much & how often
A small amount occasionally.