This is a known bug. Unfortunately, we cannot fix it, because it is caused by another app (MIUI clock app) which communicate erroneous info to Smart Launcher.
The good news is you can easily fix solve the problem by installing and using a different Alarm clock app like Google Clock https://play.google.com/store/apps/details?id=com.google.android.deskclock
This behavior is consequence of a change in MIUI 11 and it's totally independent from Smart Launcher. Now you need to enable the option Display pop-up windows while running in the background (in Settings > Apps > Rights > Other permissions) for each widget you want to use on your home screen.
You can read more details on the Xiaomi official community
At the moment, there aren’t any other known issues about Xiaomi or Redmi devices, if you find any, please report the problem to [email protected]