i tried the rom "the galaxy project" with twrp everything works,but i would like to go back to the original samsung stock,i had read about the bootloader problem,i was hoping someone had found the solution
Mixing firmwares is generally not recommended, but it has worked for me in the past. You can try to downgrade only the parts that aren't version locked.
For that, you will need to extract the tar.md5 and resulting lz4 files to get to the raw images and use heimdall to flash them individually. Good luck!