Just to add, in step 10, the chip on the right with a data matrix on it is a speech recognition sensor from STMicroelectronics that works with the microphones for noise-reduction during calling, while the chip on the left marked MHEK NYH7 is an accelerometer from Bosch that works with the IR sensors for wear detection and also probably used in spatial audio function.
A keyboard that is not separable from the body is likely a result of adding spill-proof feature to it.
It is impressive to see Google added two IR sensors for better wear detection. As far as I know only Airpods/Airpods pro has that, Galaxy buds+ also have it but it is done partly through capacitive touch sensing rather than IR sensor. The usage of BES2300 also seems reasonable as it might be the only Bluetooth SOC that has enough performance for Google to implement various features such as translation to the headset.
The thing is that rubber gaskets only work if you have some other mechanism that holds two parts together very tightly, for screws, with display and back cover glass this is definitely not feasible at all, and the adhesive isn’t there just for waterproofing but also to hold them in place.
Since there are heatpipes running all over these metal shieldings, it’s also reasonable to say that they act as a form of heatsink to even out the heat
It’s a form of electromagnetic shielding I assume. This is a very common design on smartphones but not on laptops, no idea why Microsoft does this.