As Seerah pointed out, interrupt spells do not flash like a proc themselves. Reinstalling WoW or addons will most likely not bring this back if you had it before, unless you're lucky that the addon that provided this functionality has that enabled by default.
May I suggest a weakaura I created?
https://wago.io/dynamicinterrupt
It gives a simple icon with the proc flash when your target is interruptible. It is based on Hekili's interrupt code that also shows the icon with countdown if your interrupt is on cooldown but will be available before the cast is finished. It is designed to be spec-agnostic concerning the icon and cooldown data; it should work for any character with no setup.