I updated my old REDMI NOTE 4 to MIUI 11 and it is awesome.
Most of the old phones are available for update.
Download it from below
The new interface is too cool. It has sorted my fast battery draining problem also.
The phone now charges quickly with a brand new and awesome charging animation. There are two default themes available and the 'Limitless' theme is very cool.
Go to the link below and know how to update your phone to brand new MIUI 11it also helped me in updating

https://youtu.be/zD6kTWiIGNA
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