Battery operation in background for Xiaomi HyperOS

In HyperOS (as well as in MIUI), battery optimization can restrict the operation of background apps. To disable it for a specific application, follow these steps:

Disabling Battery Optimization for an Application

Open Settings → Battery.
Go to Battery optimization (or Power saving → Battery optimization).
Tap the three dots (⋮) in the top right corner → Advanced settings.
Select Apps → find the Kolobok app.
Instead of Optimize, choose Don't optimize or No restrictions.