It's true that improper UVB will effect eating and behavior.
The starter kit with that small
UVB bulb is not enough UVB for a bearded dragon. It's sadly a dishonest practice that they put on pictures of bearded dragons and say here is your starter kit. A Reptisun T5 HO (high output of 10% UVB) with reflector that spans most of the length on top of the screen should be enough UVB. It's a lot stronger, so the 30% reduction from the mesh is countered by the strong T5 bulb, a similar T8 bulb must be under the mesh. T5 is the skinnier than the T8 and it's a newer technology bulb.
You'll also want to know that a bigger enclosure for when your dragon grows up will also be better for them to move around, exercise, be comfortable. So when you get a longer UVB tube light think about how getting a decent size can be reused later for an adequate adult sized enclosure.