How to flash BR 9.4 without any problems (most of us know but sometimes it is just a small detail thought of as routine that's enough to fail...
1. Make a full backup in Twrp and store it somewhere save.
2. Get the stock HVJ5 rom. (check for the right regional code, samfirm tool is quite helpful)
3. Flash HVJ5 in Odin (all files but home_csc)
4. Boot up, enable dev mode as well as USB debugging.
5. Go back to dl mode and flash twrp in AP slot as well as vbmeta in CP slot. (without vbmeta twrp won't boot up and you are stuck at dl mode screen)
6. Straight up to twrp. (vol+/bixby/power just like three seconds)
7. Completely reset internal SD (type yes...)
8. Flash multidisabler right after.
9. Flash BR 9.4.
10. Flash magisk apk and the corresponding patched twrp.
11. Reboot and set up magisk before logging into your accounts (Google, Samsung...), enable zygisk, flash safetynet zip, set up forced blocklist.
[12. Enable highest available swap ram in system maintenance, force reboot (vol - and power) and twrp reboot (vol+ and bixby, power until boot logo) before system reboot kicks in.]
13. Reboot to recovery, cleach cache/dalvik, reboot to recovery.
14. Be happy about the sheer poetry of a custom Rom working fine and thank starbucks2010.
15. Share your experiences with others asking for help.