Just sharing the steps I took for successful flashing of my device
0. Backed up my nudes (obviously)
1. Unlock bootloader (fastboot flashing unlock)
2. copy paste the commands line by line, use only the files from images folder
2(a). after fastboot -w I got
make_f2fs failed: 4294967295
fastboot: error: Cannot generate image for userdata
Safely ignorable, ntg wrong
2(b). any missing files, again ignore, just proceed (will appear like quite a few missing, dont worry)
3. After the last my_manifest file, I again ran the "fastboot -w" (with same output as 2(a)).
4. fastboot reboot - brought me to recovery, choose english, factory reset, reboot
After that it booted into OOS, but lock screen security didnt work
as mentioned in the thread, the solution was to keep locking/unlocking/locking till it worked
Thankfully for me it worked first time so;
5. fastboot flashing lock - voila