How to Use 'Split Screen' Feature in Redmi Note 4 running MIUI 9.5 ?
Step 1: Open some Apps that you want in split Screen.
Step 2: Tap on the 'Recent Apps' button.
Step 3: Tap on 'Split Screen' located on the top left of screen.
Step 4: Drag the App that you want in Top screen, and just Tap on the App that you want in Second screen.
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https://www.youtube.com/watch?v=yXeikNusbRQ