Mystery: where is the spoiler function???
Another angle to look at it is this:
Does a story creator lay out what is happening
OR
Does someone suggest an event or situation and the players make up how it goes?
Excessive examples, trying to get away from actual mystery and more into an as yet unknown set of actions that are likely to succeed:
Gm says there is a locked door, a chasm to cross, and a riddle based on murals in the rooms before and after the chasm. The GM lists lock picking, a movement type skill check, and perception checks as likely solutions. Being reasonable, they will also accept typical ways around each obstacle like teleport, flying, eidetic memory, lore skills, etc.
VS
The GM says there is a cleverly difficult set of tests between the players and their goal. They players then decide that there is a very difficult and trapped, locked door that leads into a set of rooms that goes nowhere. Another player suggests that hidden in these rooms is a mechanism that makes it possible to open/reveal the real door a distance away from the one they came through, so going in is still necessary. Someone says it was known there was a key to this difficult door, and it might be safer to try to find or reconstruct this key in a side scene. And that's just to get to the physical-bravery challenge ...
Another example:
GM says an enemy raiding force of some strength is threatening the city. GM decides they are crafty, and send small bands to harry people on the three routes but they know a really less known way and are moving their main force quietly through there and hope that some troops are out chasing the retreating small bands, and the main force arrives unexpectedly, they will likely take some important ground/fortifications and the situation is dire.
The players may have rolls like warfare, or scouting, or backwoods lore that they could roll to know about the possible use of the back way, or the GM could decide that the players get to decide how they allocate their forces.
VERSUS
The GM says a large raiding force is on its way, maybe even establishing what sort of force in terms of culture and technology. After that the players decide how the attack happens, and create scenes that produce the drama, tragedy, loss, and courageous sacrifices that make a good war tale. Maybe they go with the hidden attack route, but decide that there are no distraction attack bands, and ultimately scouts will report back that they didn't see an army, except those who encounter the army and likely are ambushed, but we can play that out, and either they return with the news, or the fact they didn't is the warning needed.
Players could also be suggesting rolls and letting the results vary up what happens, including adding details to justify a result, like oh there should be a lore check to see if we think of all the hidden ways, and no we failed that roll, but no one will forget that high valley that should be snowed in as a route, so maybe there are forgotten tunnels through the mountains.