How do you prevent the use of a flint and steel?

This solution gets what you want, but it will reset the NBT tag (tracks how much durability the item has). https://imgur.com/a/edLGoJN

In this case, you will want to make an item that look exactly like the flint and steel to replace the item in someone's inventory. Keep in mind this makes a completely new item when you leave, but this is what I could come up with for you short term. Just remember to make it replace the replaced item when you leave said dimension. Hope this helps you!

It should work with event cancelling, but I'm not sure why you ask while knowing the answer. The procedure is quite simple:

*player right clicks block* trigger

• if ID of dimension event/target entity is in = number_of_your_dimension AND if item in main-hand is flint & steel (you can add additional "OR" for off-hand, but I don't know if flint and steel works in off-hand):
  • cancel event