Getting a Samsung Galaxy S9+ “star2lte” with Android Oero 8.0.0 will not be easy. It would have to come out of a drawer and not be used for a long time. Realistically an S9+ with stockROM Android 9 and Android 10 is offered.
Since Jan. 2020 Android 10 is offered for the S9+. In the meantime the update April 2020 is the fourth version of Android 10.
If you have a S9+ with Android 10 with update until March 2020 at the latest, a stockROM Android 10 downgrade to stockROM Android 9 is possible. And you can switch from stockROM 9-pie to /e/ OS /e/ for star2lte dev (oreo).