So, funny thing. The game does have a dedicated pause key (space bar by default) but its' behavior is absolutely scuffed. You would think that it would be a press to toggle, but instead it's a hold to temporarily pause the combat, because after a couple seconds it will advance a tick anyway.
HOWEVER, you can use it while manually toggling combat pause with the button on the combat UI to basically achieve an effect similar to manually advancing combat a single tick. But honestly, the pause key should've been a toggle to begin with.