Reactions are an important part of 5e and one of the better parts of it.
Eithe rmake it with readied actions (like Overwatch in XCOM) or with a real time prompt.
Just be brave about this
Why not instead of prompts, you press the space bar in an apropriat emoment, this freezes time and gives you a few seconds to select a reaction?
How hard can that be in a game that already lets you pause in the middle of action
That actually brings up an interesting question about some non-reaction things... how do they do the paladin smite ability? Do you first roll for attack and then decide if it's a smite (as is the case in the 5e rulebook) or do you have to use it in advance? If they're going for the latter then I fully agree and this might be a good way to do reactions in general - press space bar to pause and use your reaction according to what you're seeing!
