Hello Menkudle,
In standard SAP REM process, Through MFBF you can't execute the Scrap backflush and Assembly qty backflush at time.
If you want to add the component scrap during the assembly backflush, you have to follow the below step. Please check below thread
Scrap rate is set in bom but can't be consumed in REM
Second Option: You can do the Scrap qty manually as per process
For Rework Process in REM:
No need to perform GR for finish material
So, You can do the only component backflush and Activities backflush with bom explode or manually enter the component and backflush.
Please check in your system and confirm the same
Regards
Umesh Mali