Great, so whatever the issue is with our relatively ancient 2017 built Stingers it's still present with cars built 2 years later.
So if Kia is acknowledging this is a problem (as some have said) they either don't know how to fix it or don't care about fixing it.
Have y'all ever seen Fight Club? Kia will apply The Formula: [Cost of issuing the recall/TSB vs. cost of lawsuits/lost business]. The Stinger is a low-volume car and a rattle-y sunroof won't lead to any lawsuits (it's not a safety concern, and it's not enough for a Lemon Law or class-action). We could potentially make it a social media stink, but I don't think there's enough of us, nor enough people who would care about it, for it to breach Kia's acceptable level of bad PR. If the PR/Lawsuit risk isn't high enough, Kia has zero incentive to help us out.
Now, that being said, I offer two stories of manufacturing defects and how they were handled by their companies:
#1: The '99-'04 Mustang had a nasty continuous whistle on the A-pillar at highway speeds. Ford issued a TSB to install little styrofoam insulator blocks around the A-pillar cap mounting pins, which blocked the wind and eliminated the whistle. It was a ridiculously cheap fix (about an hour of labor and $0.15 for the insulators). So, how did this work within The Formula? My guess is the Mustang is Ford's flagship car and also a high-volume seller, so there's way more people to get upset about it, therefore Ford has incentive to address the issue.
#2: The the first-year production 2002 Yamaha Roadstar Warrior (a muscled-up drag bike version of Yamaha's flagship Roadstar) had a bad fuel line quick-disconnect valve body. One side of the QD valve developed a leak along it's injection-molded seam. The leak got steadily worse until fuel would drip constantly down the side of the bike. Nearly all 2002 Warriors developed this leak at about 10,000 miles. The community was well aware of it and very up in arms about it. Yamaha never publicly addressed the issue, but they did quietly substitute the bad part in the catalog with an upgraded one. They didn't even issue a TSB. Any owner with this issue had to buy the part and install it or have it installed ($56 part, hour install). In this case, the Warrior was a low-volume bike, and the risk of bad PR or lawsuits was minimal (by the community's own count, this issue only resulted in one bike burning down).
If the fix for the Stinger is a cheap couple of shims or insulators, Kia might issue a TSB like Ford, or worse, quietly fix it in production like Yamaha. If the fix requires removing and replacing the headliner or sunroof assembly, I don't think there's any way they'll ever eat that kind of expense.