This pop up slows down combat, handholds you and stops you thinking. . . . This is not 100% needed feature and truthfully its out right terrible.
Sorry I don't agree. I think it increases strategic thinking. Using @Niara's example, you are facing the lich lord and his imp familiar. The imp throws a rock at you. Are you going to burn a spell slot to cast shield or are you going to take the hit so you can save that reaction for when the lich sends a volley of level 9 magic missiles at you?
Or, in Solasta itself. You are completely surrounded by undead, you turn undead and they start to flee. Are you going to have the mage try and hit the vampire with her staff -- which ends the turned state and returns vampire to battle -- or are you go going the let than one run while you focus on the undead that weren't turned. The pop up is doing something important.
And, sure, make it automatic for those who want it but I suspect that will lead people to ask "why am losing my spell slots after each battle"?
And yes, Solasta has house rules. Some are really fun. What I really like about those devs is they've started from the position of "the rules are great, how do we recreate the tabletop experience" instead of "these rules aren't well designed for a video game, we're going to have to make so major revisions.