No variant rules unfortunately according to the Fdroid. You should check out the sudoku games from Cracking The Cryptic on the Google Play store if you want that. They aren't FOSS but they have hundreds of handcrafted puzzles for a few bucks.
Your likely looking for the app "Puzzles" ob Android or one of its desktop versions, I am not entirely sure if they are actually open source but there are at least some people's contributions and it not only has "Killer" sudoku but a whole bunch of additional options (as well as tons of other awesome puzzle/logic games)!