1. I used BOOT too in addition to selecting Vendor and System/Android as per steps shared when flashing but will try flashing again with BOOT not selected
2. I used the Scatter file extracted as part of backup process before flashing the new rom. The WWr MTK 2.50 was not downloadable so i used Mtk 2.51
In this 3rd step as per PDF (Make a copy of the scatter file and preloader file that you created in previous step and paste it into 1. Firmware/…/ YT9216BF_6.2v3.5_02.05.2021 folder, overwriting those files in the folder) no Scatter or Preloader files were present in the downloaded ROM folder from the link shared.
3. Sure I am ok to share my BOOT1 file soon if it doesn't contain any personal data from the unit
4. In case it doesn't work, I will let you know and request for preloader or scatter file creation.
Thanks for getting back on this. Will share the update and details soon.