Choose version with Friend'Pass, if your friend does not have this game and the region of his account Russia/Belarus or other, in which this game is not available. If you pay extra for the Friend'Pass version, you will get an additional Steam account with a region where game is available. Your friend will be able to play with you through the version for a friend without buying full version the game. You can choose when you click the “Buy” button.
https://store.steampowered.com/app/3052150/Split_
Steam