I think it's something to do with the source code (drivers?) to go with the goodix sensor not being open source. But it works fine on LO14.1
Yes, because Redmi Note 4 got Nougat in MIUI also so no need to deal with Goodix Drivers. But as Xiaomi N...
You need to install nano Gapps for Ok Google detection...
How to use Google assistant I'm using Dec 21 build also installed pixel launcher with Google app
For google assistant you need to install Google app as hemantbeast said...