FYI:
Still no notifications on Android 9 (Pie) with 2.32beta.
(In detail: Android 9 / MI-UI 10.2.x / Xiaomi Pocophone)
As stated here [APP UPDATE: Nuki Android App 2.3.1-Beta - #5 by Matthias_Zeise]
At another device (Android 7.12 /Lineage) notifications are fine.