https://wccftech.com/samsung-galaxy-s9-galaxy-s9-get-an-unofficial-version-of-twrp/

Anyone familiar with custom ROMs will more than likely have used TWRP on several occasions. TWRP (Team Win Recovery Project) is a custom, community-driven recovery that allows you to root your device, flash third-party ROMs and a whole lot more. Very often, it is required as the stock recovery that comes with a device is highly limited in terms of what it can do and discourages users from tinkering around with their devices too much. To be fair, you don’t really need to root your device anymore, unless you have a really specific reason for it.

Despite the open-source nature of the Android operating system, companies don’t want users to mess around with their devices a whole lot and have put safeguards in place that can detect any unauthorized modifications. Samsung implemented a hardware switch that trips when you flash a custom recovery, effectively rendering Knox useless and voiding your warranty. The process cannot be reversed even if you were to undo all the changes you made to your device and you won’t be able to use features such as Samsung Pay and Secure Folder anymore.