Go to notification then advanced settings then floating notifications

Bcz kuch kuch countries me abhi tk ni ayi update april iss liye likhi kio k april me a51 ki android 11 enrollment puray world me complete ho jaye gi

Yes its working .. head to the settings app then select notifications from there you will find "brief notification setting" open that and you will find edge lightning on the top. You cam enable it from there.

it will be normal after 1 2 days

try charging your phone while powered off..because after new update phone optimize itself and all the apps in background for a day or two so the processor works continously that uses charge and maked phone lag