If you imagine that you could take a snapshot of the universe (whatever "the universe" actually is), but with the utmost microscopic precision; the exact positions of every electron round every atom, every atom with respect to every other atom, every photon, etc, etc. 100% precise capture of the physical state of that universe.
The problem is that we know that this is not a valid way to think of the universe. There is no microscopic precision. That would require a microscope to interact with and perturb what was being studied and nothing has an 'exact position' anyway. Electrons are not particles, so they are never in a place. They are actions, known to us as shifts in patterns of field potentials.
I realise this is counterintuitive but it is cast iron established fact. The only problem is trying to find a way to portray that fact when the key problem is that the dynamic elements of the universe are by definition unenvisageable. No portrayal will be right, but at least we can get away from billiard balls a bit. My fascination with Leibniz is because he understood the way quantum mechanics would be unenvisageable 300 years before the theory was created.
My way of looking at it is to say that the dynamic elements, the Planck's quanta of action that ground all physics now, are like chess moves. The elements are the moves, not the pieces. There are no pieces, so it is a bit more like chess played on an electronic screen. A any point in time you are faced with a field of values, some places having pawn value and others queen and some nul. What happens next depends on this starting pattern and a set of rules about the probability of any particular move occurring. For most of those rules there is default spatial symmetry. So, like a single king on an empty board, there is an equal likelihood of moving back or forward or diagonal or whatever. Since only one move can occur and the chances are equal the result is random. There is no other way to make the rule work.
A physics example is when a fluorescein molecule is excited by light and has absorbed a photon of energy which leads to there being an active electron orbital of a higher energy sort together with an 'empty' lower energy orbital sitting waiting to be filled. In this situation there is an equal chance of a photon being emitted in any direction from the high energy orbital, with a switch to filling the low energy one. All that is required of the photon is that it restores spin symmetry in the universe by carrying off a unit of spin to somewhere else. It is a bit like a king in check from a distant bishop. It has to move somewhere to save the universe but it does not matter where.
So for any given scenario the rules for possible futures are always in part random.
The analysis I have given is cheating because there isn't actually such a thing as a point in time scenario. But trying to explain that gets rather hairy.
With regard to the tiny time step thing, I think this is a common misconception that a surprising number of physicists have got stuck on, including Carlo Rovelli. Because energy is quantised people have thought that time and space ought to be quantised - which might seem to mean that everything is made of tiny little four dimensional spacetime bricks.
However, this makes no sense because there is nothing to define the edges of the bricks. This is where envisaging is so counterproductive. Moreover, energy is not made up of little energy bricks either. What quantum theory says is that all we have are units of action and each unit of action 'uses' a defined amount of a particular variable. So an s orbital in hydrogen uses so much energy. But for deuterium an s orbital uses a slightly different amount. You can cut energy up into whatever sized bits you like as long as they are the amount the rules say are 'used' by a particular action. The same works fine for space and time. There are no granules of time. It is just that time can only be used by actions in specified amounts. Some other action might be using the same time or space (another orbital in the same atom) but in different amounts. Time and space are 'quantised' exactly the same way energy and momentum are. In that respect things are very different from the chess board, which is why life is so messy, with everything overlapping.
