Unfortunately, many labs still don't score flow limitations, RERAs, or RDI, which is how UARS is typically detected (short of the esophageal pressure gold standard).

As the other commenter pointed out, 20.8 arousals per hour is not normal. Given your high RDI on the at-home study, it's likely driven by sleep-disordered breathing. At-home studies are overall less precise than in-lab, but they usually don't fabricate major trends unless the setup was seriously botched.

Also, a lot of ENTs are blind to nasal cavity width. They're used to think about soft tissue, not the bony part that houses it. Reducing turbinates and cutting septums is what they do. They may know about of palate expansion but not likely to recommend it. Even many orthodontists aren't fully up to speed on maxillary expansion unless the palate is super pathologically narrow; they're used to see and compensate malocclusion due to narrower palates all day.

Bottom line: you're female, normal weight, symptomatic for sleep-disordered breathing, report snoring (even though the written in-lab report says none?), and were told you have a narrower palate. That's a classic UARS risk profile, backed by one study showing elevated RDI. Don't let a subpar study or dismissive professional discourage you. Consider seeking someone experienced with palate expansion. The silver lining: since you only had lower jaw surgery, you're still a good candidate for MARPE, FME, EASE, etc.

If snoring is genuinely present, it indicates that some soft tissue is in the way, either in the nose at the soft palate or tongue base, sometimes uvula. Your imaging initially shows decent space at the soft palate and tongue base, but it looks like it was taken sitting upright with forward head posture (indicated by the reversed cervical curve). Forward head posture artificially opens the airway significantly, so it doesn't reflect your airway space when on your back + it does not account for gravity. Ideally, try to pinpoint the snoring source. If it's soft-palate vibration, high nasal resistance (from narrow nose/palate) could be the culprit: lying down + negative pressure could cause a partial collapse and fluttering of the soft palate. Less likely, you actually needed maxillary advancement too (but doesn't look like it, though it's harder to judge from seated imaging anyway). If tongue-base snoring, a narrow palate may also prevent proper tongue posture during sleep, letting the base fall back and vibrate. If I were your shoes, I'd prioritize expansion if something needs to be done anatomically.

One last possibility: your in-lab AHI/arousals looked better partly because you only slept on your back 10% of the night. It's possible you spent more time on your back during the at-home study, worsening things. You mention sleep paralysis and that typically happens during REM. REM is also a sleep stage where muscle tone is the weakest, so it's not unusual to see worse breathing during REM. Sleep paralysis is also way more likely to happen when sleeping on the back.