Any increase to the size of the object will increase the force applied to it by gravity. Increasing the thickness will cause the ratio between mass (and the associated force) and cross-sectional area (and therefore, the strain as well) to remain constant, while increasing the height will increase it. You build a tower high enough, and eventually the stress will become too high and the whole thing will collapse. There is not a lot to misunderstand here.
No, if the width and length of the building continue to increase disproportionately to the increase in height then the building can theoretically get taller forever. However since the increase in the supporting dimensions scale is not linear but exponential the total amount of material needed keeps increasing more and more to the eventual effect that basically the whole earth could not afford to make the building any taller. Therefore Square-Cube Law does not ever stop the building from getting taller, it merely makes it too expensive to make it any taller than it is by having the required amount of materials perpetually multiply.
Let us look at this scientifically; if you were right, then the largest buildings in the world would have to be made of marble and titanium; instead what we see is that they are made out of the same steel and concrete as ordinery tower blocks. We also see that elephants are made of the same flesh and bone as mice and not some kind of super flesh and bone. Yes, using stronger materials allows you to make a creature or building taller without increasing it's supporting dimensions disproportionately but I am assuming that larger creatures as in real-life are not made of stronger materials than smaller creatures.
The cross-sectional area you speak of is simply what I am calling the supporting dimensions and nothing else; that is the two dimensions other than it's height.
However small the creature is, the supporting dimensions always be holding up the whole weight of the creature; since that also includes their own weight what this means is that their material *must* always each provide 50+% extra carrying capacity on top of the weight that the materials add to the system.
If this is not the case, then the creature will
collapse under it's own weight regardless of how small it happens to be.
Since all supporting dimensions carry 50+% of the weight of the third dimension,
2*4*4 is the formula that would physically allow you to basically scale something humanoid up forever. I think a creature with more than two legs on the other hand would instead use
2*2*6, the latter being it's width, the former being it's length and the middle being it's height (what is supported). The problem is not that the creature cannot be scaled up, but that the cost of perpetually increasing the supporting dimensions disproportionately to every increase in it's height ever multiplies to the point that there is no way to get enough nutrients and energy from the enviroment in order to sustain it.