I also see Mobile Network as top app (always... on crDroid and even on Lineage and EliteROM), but the battery issue you are suffering is much worse. On lower android versions, it was "cell standby" and it was always my top app despite not using SIM data. I only suffer a few percent battery loss and deep sleep is in the 90's usually.
Here is a small laundry list I have collected regarding battery drain "solutions" on these Redmi phones: (if anyone has other suggestions, please post them here)
Run even if global rom:
adb shell pm disable-user --user 0 com.android.traceur
adb shell pm bg-dexopt-job
and firmware
The ultimate script that provides firmware packages for Xiaomi devices.
xiaomifirmwareupdater.com
and disable in Developer Options:
"Mobile data always active"
and
Turn on Data Saver under Network and Internet if you want
and these MIUI suggestions someone posted:
"Killed aforementioned bloatware's as many permissions as I could via the "Permission Manager".
Turned off Bluetooth scanning (< important).
Turned off MIUI's "Usage and Diagnostics".
Stopped apps from modifying System Settings.
Turned off Google's "Usage and Diagnostics".
Turned off "Unrestricted Data" of all apps.
Disable background access of all useless apps from "App battery saver".
Restricted or disabled background data usage of useless apps.
And of course, I also turned off Nearby Share."
You can also try disabling "Automatically select network" on SIMS and manually choose yours instead.