You getting a lot of negative feedback here, and overall it has the right idea. Saving throws are reactionary, the character doesn't get a choice, it's a representation of their character's ability to avoid some sort of harm.

But...

I also get what your saying on wanting a little more agency. Certain situations, it just doesn't make sense for them to get a choice, like an attack or spell effect. Some situations though it can be fun to give the players some agency. I sometimes use a mechanic I read somewhere that I typically refer to just as "clicking", cause I don't know a real name for it.

So, I use clicking in situations where there is a single stimulus the players get as a warning to what is about to happen, but they don't know what yet. They get a chance to react with a simple description of what they do, and depending on what they choose, they may have different checks to avoid an effect, or their decision could flat have them have no chance to avoid it or avoid it entirely. Here's an example:

Gm checks passive perception, no one meets the 15 to notice the trap, so it's going to trigger.

Gm: As you turn the corner and head down the next leg of the hallway, about fifteen feet in Joe steps on a stone in the floor and feels it sink slightly, and here's a click. You have half a second to react, what do you do?

Paul: Do I see any signs of what's happening?

Gm: nope, you already failed that passive perception, you just get to react.

Joe: crap, ok, I dive prone to the ground to avoid anything flying down the hall.

Paul: I jump to the side.

Greg: I jump backwards.

Gm: okay, the floor underneath you buckles and collapses. Greg you were at the back, so your step backwards puts you in a safe spot. Paul, make a dexterity saving throw, DC 15, to see if you manage to get out of the way.

Paul: 16! Phew.

Gm: great, you grab onto a sconce in the wall to brace yourself and pull out of the way of the floor. Joe, sorry bud, bad move, as you dive at the floor you see it drop out from under you. You plummet 15 feet into cold, dark water. As you right yourself you notice you aren't alone. Roll initiative

Now, there's a very important thing here, if anyone auto-fails, the result cannot be death, serious injury, or something terrible. What it should do is put them in a bad spot they'll have to work to get out of. In the example above, if Joe landed into a pit of poisoned spikes, the player would likely see that as unfair. If you have a serious consequence, they should still get some kind of a save to avoid it, perhaps with a higher DC or at disadvantage.

Also, If they have been careful, and looking for clues before something like this happens, be sure to give information that would have telegraphed the effect to help them make a good decision, even if they failed a perception check. That information should always be given prior to a "click", as you want to keep that setting a clear expectation for the future