Whether it was purely stylistic or intended to make the game behave better on older consoles, a lot of people found Mortal Kombat 11's halved framerate during cinematic attacks distracting. Previously only available via mods, today NetherRealm Studios patched in an official set of 60fps options today for menus, cinematics (including fatalities) and the Krypt. They do warn that the Krypt toggle is only for truly high-end PCs. Below, for illustration's sake, a comparison video letting you see the two framerates side by side, albeit captured using the unofficial 60fps mod.
Ever since NetherRealm dusted off the Mortal Kombat series with their initial, un-numbered reboot (it's still MK9, though), they've capped the more cinematic moments of the game at half of the normal action's framerate. It definitely gave them a more dramatic, movie-like look, especially in the gleefully over-the-top Injustice games, but it is a very visible switching of gears. As today's update makes the higher framerate mode official, you should be able to play online against others no problem, whereas the mod solution was running the risk of being flagged as a cheater.
Credit to "RajmanGaming HD" on YouTube for the clip.
They have made it a separate toggle to enable 60fps when exploring the Krypt. The unlock hub and weird side-adventure mode pushes hardware significantly harder than the base game, so you'll need a beefy GPU to hit consistent performance there. I've heard reports from MK fan friends that the game becomes crash-prone when running the Krypt uncapped. Your mileage may vary, of course, but you have been warned by both players and the developers themselves.
There have been some complaints that the game is limited to running at a mere 60fps, not supporting modern high refresh rate monitors. While I can understand the complaint, I'd be very surprised if that changed. Competitive fighting games traditionally time actions by frame counts, and adjusting how many frames there are in any given second throws a spanner into the works. Mortal Kombat 11 in particular introduces frame timings in its own tutorial, so sixty is as good as we're going to get. Still, can't deny it looks lovely as-is.
You can see the full patch notes here. If you're delving down into the Krypts today to flex your PC power, check out Dave Irwin's guide on where all the best loot is hidden.