[Cupid][Android 12] Downgrade from Android 13 to Android 12 issue (IMEI lost)

[ciubex]

Can you please advice me what steps should I take into consideration to have a fully working Android 12 version on a Xiaomi 12 (cupid) phone?

I tried to downgrade the phone firmware from Android 13 to Android 12 (xiaomi.eu_multi_XM12_V13.0.41.0.SLCCNXM_v13-12) but both IMEIs are not recognized (show as 0).
If I'm flashing back any of Android 13 versions (Miui 13 or Miui 14) the phone is fully functional, the IMEI is "recovered".

I tried to flash manually modems images from newer versions but I have same issue, I used below commands:

fastboot erase modem_ab
fastboot flash modem_ab modem.img

I also tried some steps from different tutorials to change IMEI, but the "diag" (diagnostic) connection on any of Android 12 versions is not stable, so I cannot use it to backup qcn file or similar.

I tried official images with Android 12 (V13.0.*.0.SLC*XM) with same "IMEI lost" behavior.

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Update: the solution is on post #6.

 

[ChupiPlum]

Did You flash the official firmware from Xiaomi with mi flash ?

Enviado desde mi POCO X3 NFC mediante Tapatalk

 

[ciubex]

Yes, I used oficial MiFlash tools for flashing stock firmware (fastboot versions).

 

[ChupiPlum]

Well i don't know how to help u then , did You Made a backup of the EFS folder on any previous ocation?
In my understanding flashing the official firmware with mi flash should do it , if not tried to go back to the first version of miui/android that your device came with and check

Enviado desde mi POCO X3 NFC mediante Tapatalk

 

[ciubex]

The phone is not dead. I mean if I'm flashing any of Android 13 versions, custom like xiaomi.eu or official stock firmwares, both IMEIs appears back. I guess the modem is actually the issue.
The first official stock firmware version was: 13.0.13.0.SLCEUXM, but I didn't find it.
I'm using this site to get stock firmwares: https://xiaomifirmwareupdater.com/archive/miui/cupid/
Anyway, my goal is to have flashed on the phone any of xiaomi.eu custom rom with Android 12, but I tried official firmwares to check if I have same issue with missing IMEI.

As a note, when I unlocked the bootloader, the phone was already upgraded to Android 13 (13.2.6.0.TLCEUXM). I didn't tried to flash an older firmware in that moment.

 

[Nuschi]

Flash the Stock Android 12 Recovery for cupid - Boot to Recovery - wipe all Data and reboot.

it is not enough to erase the data with the "MiFlash" program. You have to boot into recovery manually, delete all data there and restart the device. Now the mobile signal and the IMEIs are back.

 

[ciubex]

Flash the Stock Android 12 Recovery for cupid - Boot to Recovery - wipe all Data and reboot.
[...] Now the mobile signal and the IMEIs are back.

Finally! Thank you very much @Nuschi!
I confirm that your steps fixed my issue with missing IMEI, I don't understand why if I'm using MiFlash or directly if I'm using bash scripts don't work.

I flashed fastboot stock version V13.0.10.0.SLCEUXM, I didn't used MiFlash, I used the flash_all.bat bash script into a Windows terminal (command prompt).
I have locally installed already drivers and platform tools for adb and fastboot, all from Google official page.
I picked above mentioned stock version randomly from the table from this page.

Now, it's time to move back to xiaomi.eu

Again, thank you very much for your solution!