This is straying off-topic, but ....
...Mechanical shutters are always global shutters. The mechanical shutter is found in DSLR cameras and as far as I know refers to the glass mirror inside the camera that flips up or down to let light fall onto the sensor all at once, completely eliminating the rolling shutter distortion because the sensor is read all at once.
....
Sorry but would beg to differ.
The mirror, if fitted, moves out of the way before the shutter is triggered.
If the shutter was effectively taking away and replacing a cover, then the first part uncovered might receive more illumination than the last piece uncovered. Also it is harder to get a mechanism to accurately reverse at high shutter speeds.
What is often done is to use a pair of shutter blinds (see image below). The first blind (the green one) 'drops' and uncovers the film or sensor; it is closely followed by a second blind (the blue one) which re-obscures the sensor. As the first blind goes 'down' it is uniformly followed by the second one so as the 'gap' travels down the sensor, all parts receive an equal duration of illumination. The gap between the trailing edge of the first shutter and the leading edge of the second one determines the exposure time.
If your exposure is, say 1/500 second, it does not mean the whole sensor is exposed in 1/500 second, it means that the second shutter is following 1/500 second behind the first - it may take well more than 1/500 second for the 'gap' to travel from top to bottom of the sensor. This means that there
is a rolling exposure (as Yoann alluded to) - albeit far lower magnitude than some electronic-only shutters with rolling readout over many ms.
Dave
https://i2.wp.com/digital-photography-school.com/wp-content/uploads/2011/07/Curtain-Action.jpg