Not sure what you mean by "not shared". First of all, you don't have to remove the frunk to see that area. You only have to remove the access panel (see page 13 in ERG): https://www.tesla.com/sites/default/files/downloads/Model_Y_Emergency_Response_Guide_en.pdf Second of all, even without removing that panel, there are obvious differences. Here's the old one. You can see clearly only the left part in the picture has holes for air to go in (the other part is sealed and looks different). There are two vertical lines that go through the section with airflow and no lines on the side that does not. Tesla Model Y Photo Gallery Shows Huge Trunk & Frunk Cargo Space Here's the China Model Y. Although I was not able to google a picture that showed if the entire thing is vented all across, there is an obvious change. There are 4 vertical lines and it spans across the whole thing (not just to the left side). 特斯拉Model Y与全新Model 3首次亮相成都,来看看有哪些黑科技 In the process of looking, I did find a video of a China Model Y frunk install, but unfortunately it doesn't show the venting situation of the access panel, although it does show how to remove the access panel (at 58 seconds):
You must not be living on the West Coast while the fires are causing smoke so bad that lung damage is a problem.
Note the whole "bioweapon defense" mode as modeled after hospitals, which rely on negative pressure to keep harmful viruses from escaping the room, even when you open the door. It does not rely on being 100% air tight all the time. The car version basically the flip version: basically with the fan running at full speed, the inside of the car has a positive pressure. So any outside air has a very hard time trying to get into any cracks. And when you open the door window, the pressure pushes air outward, preventing it from entering the cabin. Also note we aren't talking about preventing toxins that will kill you even with a single molecule (that is when airtightness may be required). The goal is simply to filter the air enough that the air is safe enough to breath as the pollutants are diluted enough that it's proportion is relatively low. This applies to viruses also. When they are diluted with enough air, there's not enough of them to infect you.