Hi from 'Down Under' Australia henklbr, 
INTRO:
On reading some of your threads for answers I'm impressed with both your knowledge and willingness to help others in difficulty. I'm new to firmware updating on Androids. However, I understand the basic concepts as have a Wintel server engineering background. I've also done a lot of research over last week and feel ready to perform my first and now essential Android flash!
REQUESTS:
I'm hoping you will be willing to cast you expert eye over the phone details uploaded for my help my S9+ SM-G965F purchased here in Australia and have uploaded jpg's with detail.
- Barneys_S9plus_Settings.jpg
- Barneys_S9plus_version.jpg
(I can't work out how to upload. Sorry.
)
- Have I downloaded correct firmware for my phone as indicated further down?
- ditto for ODIN version and USB drivers?
- Is there anything else you might suggest to ensure a successful downgrade from Android v10 to latest Android v8?
- Am I correct that flashing with v8 firmware won't trip the warranty cancelling Knox e-fuse or prevent later OTA Update back up to Android v10+ if a call recording issue is addressed by a later Samsung update?
- So long as I don't brick my phone or trip the Know e-fuse I should be able to use ODIN to flash back to later Android v10 firmware if needed?
THE REASON:
I find I am forced to do this as an essential call recording app won't work on the latest latest Android v10 or earlier v9 I had used OTA to update thru before restoring all apps and data etc. This discovery was a bomb shell as I have a permanent disability that prevents me taking notes whilst on a call so a call recorder is a must.
In troubleshooting I discovered Google had removed required permissions from Android 9 and up. The only solution is to either root or downgrade to latest Android v8 - and Samsung Support told me it could not be done by owners!!!
Then after much research I discovered SAMMOBILE's excellent resources, obtained foot in the water subscription and decided to have a go in earnest. I'd sure like to prove Samsung Support incorrect 
CORRECT SAMMOBILE FIRMWARE?
I've already downloaded from the firmware archive what I think are my current Australian S9+ v10 and latest target v8 firmware versions:
- Current : 10_G965FXXU8DTC5_G965FOXM8DTC6_XSA.zip
- Target : 08_G965FXXS2BRJ6_G965FOXM2BRJ3_XSA.zip
Other ODIN support files:
- Odin3-v3.14.4.zip
- SAMSUNG_USB_Driver_for_Mobile_Phones_200429.exe
PROCESS STEPS:
I've also noted your basic tutorial found in thread 13. https://www.sammobile.com/forum/thre...light=SM-G965F
How to flash firmware to your phone:
- Extract (un-rar) the firmware file (i.e. to folder c:\Odin) ***
- Download Odin3-v3.14.4
- Extract Odin ZIP file (i.e. to folder c:\Odin)
- Open Odin Odin3-v3.14.4
- Power OFF phone
- Reboot Phone in Download Mode: push Bixby + Volume Down + Power buttons, follow instructions screen (PowerUP), connect phone to PC with ORIGINAL USB-cable
- Wait until you get a blue sign in Odin
- Add the firmware files to their designated slots
Put ALL 4 files in the desired slots at the same time in Odin
BL -> BL
AP -> AP
CP -> CP
CSC or HOME_CSC -> CSC
Note regarding CSC-files:
CSC_OXM -> phone will be WIPED/RESETTED
HOME_CSC_OXM: data will stay intact
- 9. Make sure re-partition is NOT ticked
- 10. Click the start button, sit back and wait few minutes
I do hope my long post is not an annoyance but I'm new to this and in trepidation!
would really appreciate your expert guidance - before I push that fateful button from which there might be no going back!! Gulp. 
Best regards,
Barney
From 'Down Under' Australia