It hasn't been long since I joined the ZenFone Max Pro M1 forums and since then I was worried about the EFS/IMEI because it is very complex in the Snapdragon SoCs. So all you need to do is to backup EFS partition by using an app created by @wanam
1) Unlock your bootloader (will be available soon)
2) Flash TWRP (if available)
3) Root your phone (Magisk/SuperSU)
4) Install Partitions Backup & Restore app from Google Play Store
5) Back up MODEM, MODEMST1 & MODEMST2 (In simple words, backup the yellow highlighted partition)
- The backups are saved on /sdcard/PartitionsBackups.
- DO NOT leave the EFS/Modems backups on your sdcard, MAKE SURE YOU KEEP IT IN A SAFE PLACE
- DO NOT use the restoration feature for tests purposes, it is recommended to use it for small partitions only (EFS, Boot, Modems.), you can restore other partitions backups with FASTBOOT.