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
MIUI 11.1 - 9.11.21/22
Xiaomi European Community | MIUI ROM Since 2010
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]