If you just bought a Samsung galaxy S9 Plus and thinking of installing third party (custom) ROMs on it, you will have to get hold of its TWRP, which is a custom recovery. This will pave the way for installing all those amazing firmwares available on the xda developers.
Keep in mind that once you have installed TWRP custom recovery on your Galaxy S9+, your warranty will be voided as it trips knox to 0x1. Also, it is meant to be installed on only SM-G965F/FD/N exynos variants only.
Installation instructions for installing Galaxy S9+ (Plus) TWRP recovery are given below.
0. Make sure you enabled developer settings by pressing the build number several times and have the OEM unlock enabled 1. Boot into download mode by pressing: bixby, volume down and power 2. Download the latest Odin version, open it 3. Download the recovery file from below and put it into the AP tab. You can download it from here. 4. Untick “auto reboot” in odin and flash the file 5. After flashing, boot into twrp. Make sure to NOT allow system to be modified till you disable dm-verity! (otherwise your phone will be stuck at bootloop). Alternatively flash my stock patched kernel to the boot partition (install, install img, check the kernel, check boot partition, done). Find the patch kernel here 6. To disable encryption you need to format data