The double-folding device looks to be in the prototype phase, as the folding creases are still visible. In its default state, the screen seems to have a 3:2 ratio, while the folded state shrinks down to a 2:1 ratio. What really impresses is the responsiveness of the Android interface that immediately snaps into the new ratio as the phone enters in the folded state.
https://www.notebookcheck.net/Xiaomi-co-founder-presents-double-folding-smartphone.397281.0.html