The update, weighing just under 1GB, based on Android 10, changes quite a bit about the Mi 10 Pro. MIUI 12 has new flatter icons, a new font, new smoother animations and a new control center with quick toggles (a swipe from the upper right corner). You also get Google's navigation gestures, the option to add an app drawer and new live wallpapers (Xiaomi calls them Super Wallpapers). A more sophisticated dark mode that can dim the wallpaper and floating windows are also part of the package.
Xiaomi MI 10 Pro MIUI 12 changelog
The update is live in Europe, but it may take some time to reach every unit.