Awww he’s a little balloon. Does he puffs up like this all the time? I don’t actually see anything out of the ordinary here. beardies do get darker when they wanna absorb more heat, only if he’s that dark all the time then it’s a problem.
If you can list his usual temperature on the basking spot and on the cool side, whether you use a probe thermometer to take these temperatures, also how many hours the lights are on, that’ll be great. Also the uvb brand and bulb information, cuz you wanna make sure these things are correct first, then you can make adjustments.