I dare to disagree Niara ... people should have option to make bad decisions, just bcs they want to ...
I dare to say that i can understand how accepting or denyal of every single possible reaction can seem tedious to people ...
So even tho i kinda hate to promote myself this way ... but i will anyway

... i believe that implementation of "Ask" is best way in here ...
For example, Hellish Rebuke ...
You want to use it when that ugly big Bugbear will attack you, bcs it will reduce his HP to half ... you dont want to use it on puny goblin, bcs most likely 3/4 of its damage would be wasted.

Therefore you set it on Ask ... and if you deny that you dont want to use Hellish Rebuke on Goblin attack, but save it for later ... you can ...
On the other hand, when that puny goblin will run around you, you can use AoO automaticly (yes i know it will make your Hellish Rebuke inactive for the rest of the round ... or more likely i presume it will

) ... but you certainly should have that option.
If you simply forbid people to make bad decisions by making all reactions as in Solasta ... many people would be frustrated, bcs they will find it tedious and anoying to have to decide every single move ...
If you allow them to keep some automatic, as they want ... they will probably eventualy find out that its much more benefitial for them to set it all to popup approval ... or they dont and they will not play effectively, but they will have fun and that is most important. :P