The Y5250H 2029 K8QEZ is the z-axis gyroscope, with zero-output center at 1.5V. The resting noise seems to be less than my oscilloscope’s background noise of 2mV. (iFixit mistakenly identified this as a 3-axis gyroscope, but testing with an oscilloscope revealed it to be 1-axis only.)

EETimes Asia identifies this as an STM LY5250 accelerometer, for which there is no available chip doc.

Resources:
Table of notable pins