With the most recent patch to UnMetal, the Ironman difficulty became a modifier for each and every difficulty. Originally, Ironman was just a modified version of Hard. Since it was already unlikely that anyone would run Ironman and it being a modifier doesn't mean much for the speedrun, it has been removed from the leaderboard. While it is possible to play Ironman as a difficulty on older patches, it doesn't make much sense to incentivize it.