Here are some tips to keep Biz Daemon running in the background and it can prevent your Xiaomi devices to appear offline.
The steps may vary due to the variety of devices, MIUI versions, or Android OS versions.
Keep Biz Daemon running in the background
Go to Settings > Manage apps > Biz Daemon > Permissions > Start in background, tap Accept
Allow Biz Daemon to autostart in your device
Go to Settings > Apps > Manage apps > select Biz Daemon > enable Autostart.
Disable Battery Optimization for Biz Daemon
Go to Settings > Apps > Manage apps > select Biz Daemon > Battery Saver > tap on No restriction.
Lock Biz Daemon on the recent page
Tap on the Recent button (The icon may vary depending on the OS version) > long-press Biz Daemon > tap on Lock this app > you will see a Lock icon on Biz Daemon.
Keep WLAN or Mobile Data on during hibernation
For WLAN Connection (Wi-Fi): Go to Settings > WLAN > Advanced setting> allow Always keeping WLAN on during sleep.
For Mobile Data: Go to Settings > Battery & performance > tap on the gear icon > select Never on Turn off mobile data when device is locked.
To enable Developer options, please refer to the manufacturer manual.
Go to Settings > Additional Settings > Developer options > Background process limit > tap Standard limit