I'm not sure they will even be able to do 5e TB exactly. My understanding ( not a PnP player since 2e ) is that you can have 1 reaction per turn, but there could be many opportunities to take that one reaction. So the game would effectively need to offer each player a reaction every time one became possible, until the reaction is taken. That would make an already slow combat experience even slower.
I believe that reactions will be automatic. Probably something like a menu players can open on their turn which will let them select which reaction (or reactions) they'll look for, and what the trigger will be. If the trigger is met, the reaction will be used automatically.
Yes, I understood something like that was the case; but issuing ahead-of-time orders is not the same as PnP where every possible reaction is considered by the player as the opportunity arises. It could also become tedious to manage triggers for things that *might* happen every turn...or might not. Selectable triggers with automatic activation also still leaves room for getting it wrong. For instance, as the enemy characters take their sequence of turns, you may change your mind concerning your "reaction orders", but no longer be able to influence them.
An alternative might be for the player to have a "reaction panel" UI element pop-up when the enemy is taking their turn. This might be something like a ribbon-bar of icon-buttons, one for each of the reaction types. All would be grayscale and not selectable until an enemy action made a reaction possible, at which point the icon-button for that reaction would light up in a coloured version for a short period to indicate you can click the button to take that reaction.
I'm not sure if that is a practical idea, as in single-player you might need to monitor 4 reaction panels at once, or whether it's a bit too "real-time" for some turn-based players. It seems to me that it would give you a more PnP-like control/choice with less needless management, and also give you more engagement while the enemy characters are taking their turns, which may improve the game-play experience.
