Welcome to the forum!
First off, s/he is very cute
There could be a few things affecting his appetite so I will run through a few things:
:arrow: Relocation Stress: You mentioned your little guy moved from a busy room to a quiet room. Even a small relocation in the house can affect them, making them have to readjust to their new surroundings and their appetite would also be impacted.
:arrow: Bulbs: From photos of your setup I am seeing a CHE (ceramic heat emitter), a red bulb, and a white bulb. The white bulb should be their basking bulb, producing a nice white light as dragons do see in color. The red night bulb is unnecessary and this will disturb their sleep as they prefer pure darkness. If it gets colder at night, the CHE you have is more efficient. Sleep troubles can cause appetite issues.
:arrow: Heat: The lizard is so little in that big ol' enclosure! How warm does his basking spot get? How do you take this temperature? Ideally, 110 degrees for a youngin' is what you'd want with a gradient. Colder temps will not allow them to digest their food properly, causing their appetite to suffer.
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UVB Light: I see you have him in direct sunlight which all dragons love the windows! But remember this direct light is still being filtered by the glass on the windows and enclosure and the dragon is not actually benefiting from this location health-wise. I do see you have a long
UVB light on the top of the screen as well. What type of UVB is it? Are you able to get this UVB closer to your dragon, or your dragon closer to this light? It is completely necessary for his health and could impact more than just his appetite. Yes, screens do filter out some of the UVB, making them less effective at greater distances. Easy fixes are to mount the UVB inside the enclosure or move him closer to the light.
:arrow: Parasites: As you mentioned, the pet store recommended a vet visit for parasites. While a vet visit to get a health check up is a great idea, and yes parasites are very common in dragons, I think the things listed above are more likely to be impacting his appetite for now. But by all means, a vet visit is a great idea anyway to make sure he's in good health!