I want to downgrade my Samsung Galaxy S9 (SM-G960U) from Android 9 PIE (firmware G960USQS5CSEB) to stock Android 8 OREO (firmware G960USQS3BRK2). From what I have learned the bootloader versions must be the same before flashing.

Can someone confirm my understanding and/or is there any other options to downgrade back to Android 8 (Oreo).