(...) My fear with a pause is that it would be like... In Solasta. I love this game but those pause appear more than once on every turns. I can deal with it but I don't think lots of players would like this.
The reason you see many pop-up questions in Solasta is because it is *not* only for Reactions. If you play a Paladin, every hit ask you if you wish to smite. It is too much.
Reaction options are more rare : Shield spell, Batte Master Riposte, and a few rare others. For many parties, there will be no Reaction options, so no pop-up: just a standard Attack of opportunity (once per round, so there is a choice there if many enemies are in reach).