GSM Arena reports:
The Mi Mix Alpha also has a 12MP camera with 2x optical zoom, though by the looks of it digital zoom from the monstrous 1/1.33” main sensor will work quite well too. Especially when zooming in at night, that f/1.7 aperture will help the sensor collect as much light as possible. Pixel binning will increase image quality even further, producing 27MP shots.
...there’s almost as much screen on there as on the “front”. This means that you can snap selfies with the main 108MP camera or you can use the 20MP 117° ultra wide camera.
I'll let you follow the links, though I agree with GSM Arena that at over £2000 this isn't a phone that is intended for serious production or retail. Not least because of the unique 'two-sided' display approach.
The 108MP sensor itself will get put into other phones in the next year, of course, though even Quad Bayer 'pixel-binned' 27MP photos are WAY too high resolution for consumer use. Maybe there will be a further reduction to 7MP general output, with every output pixel being averaged from 16 sensor pixels, and with genuine 7x 'PureView' lossless zoom. Making me think, as GSM Arena did, that the inclusion of a 2x telephoto is pretty pointless!
Anyway, we live in interesting times.