I'm sure I've said it before, but I have my own idea for reactions, which combines elements from both Solasta and BG3 ways of doing it.
1. PC's can toggle what reactions they prefer, but there are still always reaction pop-ups. What the toggles do is set the default to either use or don't use. Example: a Wizard has Shield as "yes" and Opportunity Attack to "No". 2. When a reaction is triggered, players have 6 seconds to respond - that helps keep things speedy for multiplayer. 3. If players pick a choice, either use or pass, it happens immediately in both cases. 4. If the players instead wait for the 6-second timer to elapse, the default reaction gets used. If the prompting action is an archer shooting which will miss the Wizard's AC + 5, the Wizard will by default cast Shield using the lowest available spell slot. If the prompting action was a goblin running out of the Wizard's melee, the Wizard will do nothing.
This solution gives the players flexibility to use their resources how they want, and the timer on the reaction keeps the action moving fairly quickly even if the player has stepped away.
***
I have to say that I also like Solasta doing automatic Arcana checks when a spell which could be countered is going on. If the player passes the Arcana check, the Counterspell reaction prompt identifies the spell, letting you decide to take it or counter it. If you fail the check, all the reaction prompt says is "X is casting an Unknown Spell", and you have to gamble on whether it's worth the Counterspell usage or not.
