Xiaomi
Battery Optimization Settings for Individual Apps auf Xiaomi
MIUI decides for every installed app how much freedom it gets in the background. Apps marked as optimized get frozen or restricted once the screen is off, which saves battery but can delay notifications or stop location tracking. Apps set to don't optimize keep running freely, which fixes missed alerts but costs more battery overnight.
You control this per app under the special permissions menu. Go to Tap on Settings ➔ Tap on Privacy protection ➔ Tap on Special permissions ➔ Tap on Battery optimization ➔ Open the Menu ➔ Tap on All apps.
From the full app list, tap the app that is causing trouble. Choose Optimize to let MIUI manage it aggressively and save battery, or Don't optimize to let it run unrestricted, then confirm with Done.
Set chat apps, alarm clocks, or fitness trackers that rely on constant background activity to don't optimize. Leave rarely used apps on optimize to reduce overall battery drain.
If notifications still arrive late after switching an app to don't optimize, check the app's own notification and autostart settings as well. Battery optimization only covers system-level background limits, not app-internal sync intervals.