It has nothing to do with Android 9/10. It's a new icon Xiaomi adopted to all of their MIUI 11 releases.
The old icon was made up of image files, then they changed it to be a vector defined as a string resource (basically, text) and all of its attributes are stored as dimens (sizes) and integers (other numbers). The new icon is also a vector, but it's completely reworked and the attributes were changed. There is no going back except using an old ROM.