Once the update is downloaded the infotainment board waits for the car's main systems to be available and then updates those as well - it's the whole 'Over The Air Update' that marketing loves to push - and why many think it's doomed to cause failure or safety issues.
That is not a satisfactory explanation. My phone uses an A/B system where if an update doesn't boot, it can simply boot the prior version. Why is Stellantis too incompetent to do the same thing with PCMs, which are much more important? Who the fuck is still buying vehicles from these clowns?
Actually, I know who, otherwise smart people who just have insufficient experience with modern cars to know what's going to be shit. One of my coworkers bought a Mach-E, I've discussed it before, he returned it because it got nowhere near the advertised range in even slightly cold conditions (like 50 F) and then he got... sigh, a Jeep. One of his HID headlight capsules recently went out. On one side it's easy to replace, there's plenty of access. On the other side the common wisdom is to remove the fender for access because it's such a clusterfuck.
If you buy a vehicle from Stellantis, you're gonna have a bad time.