What I did was factory reset once for installing pe rom, it didn't helped so I did once again it deleted all data and successfully flashed rom without wiping via adc(pc). And about backup, I was able to back up and since in my old device we simply had to backup data, system and vendor , and its something new to me with a/b partition amd super etc. So, I had to test it, but I did successfully flashed the boot img from the backup, so I guess rom restoration is possible too. I will let you know later.
Have you flashed TWRP to the recovery partition or just booting into it via fastboot?