"Movie magic" doesn't really create impossible situations it rather produces the illusion of them.
The classic example would be that of continuous motion itself. Like what you experience on screen is perceived as a continuous evolution of events. But in reality it is not, it is a rapid sequence of single pictures, that is fast enough so that we don't see the gaps in between.
Though what that means is that what is shown on the next frame does not depend on what is shown on the previous frame. The connection between them is not a matter of logical consistency but of the viewers expectation that they are connected. The magic isn't happening on screen it's happening in your brain because you run out of options to explain what you see, so you either have to give up the idea that these events are logically connected or you have to accept that there are some supernatural forces at play that do not need to adhere to logic (or to a different one).
Or you again cheat and use the fact that this is all overwhelming and that the intuitive reaction to that means to narrow the focus away from the entire universe of concepts where this would lead to contradictions and towards a particular scene and within the limited focus of the observer you've got a lot more leeway to push all the contradictions to "the off (-screen)" and if they aren't relevant to the story just ignore them.
Also that is not a novelty of CGI that already happens with regular special effects (SFX), and we call these contradictions "plot holes". In some cases it literally renders the events on screen impossible even within the set of rules of it's own universe, but as that is outside of the focus of vision of the observer we usually tend to ignore it, similar to how we tend to ignore that these things are in contradiction with the rules of our own universe.
and in terms of a squared circle, well think of a single pixel, it's both a square and a circle, depending on the context and it certainly has the same size.