I tried your steps but after step 5 I can't get into recovery mode.For those who are facing problem during installation.
1. Follow this step if you are not on any twrp recovery.
Connect to PC in fastboot mode and boot into nebrassy twrp recovery and install orange fox twrp recovery.
2. If twrp is already installed then flash orange fox twrp recovery.
3.Install OOS11.x.x official twrp flashable zip,then install orange fox recovery and boot into recovery.
4. Follow step 3 once more.
5. Now Install syberia rom and flash orange fox recovery and boot into recovery.
6. Install fw-firmware zip and flash gapps, magisk (optional).
7.Now go to Factory reset in recovery and format data 'yes'.
you are good to go with syberia os 12.
It just stucks on Orange Fox boot logo, I also tried to boot twrp from fastboot and also is stucked on TWRP boot logo.
Can somebody help me?