Samsung’s One UI is a pretty great update and brings along a bunch of new features as well as a major UI redesign. The user experience; however, still is way different than what you would find on a stock Android device such as the Google Pixel devices.
Samsung has managed to clean things up a bit with One UI but if you’re a stock Android kind of guy, then you’re in for a treat since the Pixel Experience ROM and the unofficial LineageOS 16 ROM are both now available for the S9 and the S9 Plus on XDA.
Nonetheless, both these ROMs are based off Android Pie which is great since there were basically no Android Pie ROMs available for the S9 and S9 Plus.
The developers say ROMs were built from source rather than using a GSI (Generic System Image). According to the developers the ROMs are fairly stable and do not have any bugs.
Downloads and more info: