[Samsung Galaxy S9 & S9+ Cross Device Development] digimuse:
I wanted to share my experience in successfully installing TWRP on a new Galaxy S9 Plus (SM-G965F/DS).

My new phone came with:

Product Code: SM-G965FZBGBRI

Active CSC Code: BRI [Taiwan]

Bootloader Version: G965FXXU1ARB3

PDA Version: G965FXXU1ARB3

CSC Version: G965FOXM1ARB3

I am using the phone with T-Mobile in the US.

I followed the instructions in the original post, with a slight variation. I added a "Preliminary" step, to do as much work as I could ahead of time, to simplify the tricky task of installing TWRP.

<sorry - I tried, but I was not allowed to post any outside links. See original post>

Step 1. Preliminary work: On a Windows PC

download & install Samsung Drivers for Windows

- download standalone driver package

- extract the .zip file, and run the .exe

download & install latest Odin (should be Odin3 v3.13.1 or later)

- download Odin (Samsung's Flash Tool)

- extract the .zip file

download latest TWRP tar image

- download from TWRP for Samsung Galaxy S9+ (Exynos)

(I downloaded twrp-3.2.1-2-star2lte.img)

download dm-verity and force encryption disabler

- copy this to a micro-SD card (will insert in phone later)

optional for me:

- download latest LineageOS and copy to micro-SD card:

lineage-15.1-20180418-UNOFFICIAL-star2lte.zip

- download latest addonsu and copy to micro-SD card:

addonsu-15.1-arm64-signed.zip

Step 2. Install TWRP on phone using Odin

Turn on phone, perform initial setup (I did not sign into any accounts)

Go to Settings -> About device. Tap 7 times on Build number to enable Developer options

Wait for approximately 7 days

- don't reboot phone, don't take out SIM card, don't turn off data

Go to Settings, remove all Samsung and Google accounts and if your device is registered to an enterprise, de-register it

- I did not have to do this step, as I never signed into anything

On the PC

- run Odin .exe as administrator

- select the TWRP .tar file in the AP slot

- all other slots are empty

- did not change any settings in Odin

On the Phone, go to Settings -> Developer options and enable OEM Unlock option.

- I was not asked to do a factory reset when I enabled OEM unlock - but you may be

(get into Download Mode)

Reboot phone in download mode: right after enabling OEM unlock

- Hold [VOLUME DOWN] + [BIXBY] + [POWER] for approx. 15 seconds

- press [VOLUME UP] to get into Download mode

- near the top I saw:

SYSTEM STATUS: Official

FRP LOCK: OFF

OEM LOCK: OFF

connect phone to PC via USB cable (had to use USB cable that came with the phone)

- you should see a Blue entry in "ID:COM" near left side of Odin screen

- if not, stop. Have to fix this

OEM Unlock is not enabled, or Samsung USB drivers are old, or Odin is old, or USB cable is bad, ...

Hold [VOLUME UP] + [BIXBY] + [POWER] on your phone and then press Start on Odin

- need another helper to press the Start button in Odin

Wait for the phone to reboot into TWRP: (around 20 seconds for me)

- DO NOT release [VOLUME UP] + [BIXBY] + [POWER] or you may not reboot into TWRP

- if you screw up, you have to install a stock ROM with Odin, wait 7 days, and try again

Step 3. Initialize TWRP:

If you completed Step 2 successfully, you should be in TWRP now.

TWRP will ask you if you want to allow system modifications - select "Keep /system RO"

Go to "Wipe" menu of TWRP and you will find "Format Data". Press "Format Data" and type "yes" to continue

Go to "Reboot" menu and Press "Recovery" to reboot into TWRP

TWRP will ask you if you want to allow system modifications - select "Keep /system RO"?

- this was not mentioned in the original post

Copy the special dm-verity and force encryption disabler zip to the phone

- can use USB connection to the phone on the PC (S9+ should show up as a device), or

- insert micro-SD card into phone (I installed the micro-SD card at this point)

Go to "Install" menu of TWRP and flash the dm-verity and force encryption disabler zip.

TWRP is initialized and fully functional at this stage.

Optional Step 4 for me:

While in TWRP from Step 3:

Backup current ROM

Go back to main menu in TWRP

Install LineageOS and and addonsu

- Select Wipe and then Advanced Wipe

- Select Cache, System and Data partitions to be wiped and then Swipe to Wipe

- Go back to main menu, then select Install

- Navigate to the LineageOS .zip package on the micro-SD card

- Follow the on-screen prompts to install the package.

- (Optional): Install any additional packages using the same method.

Note: If you want any Google Apps on your device, you must follow this step before the first reboot!

- Root the device by installing the addonsu zip package on the micro-SD card

- return to the main menu in TWRP

Backup the newly installed LineageOS ROM with addonsu

Reboot system

The phone appears to work with T-Mobile in the US. I've only tried it for a few hours.