Say you have a giant, similar to those of Dungeons & Dragons. For the purposes of this question, we'll say it's twenty feet tall. Is there any way one can alter its anatomy to save it from collapsing on itself due to the Square-Cube Law while keeping a basically humanoid shape?
For twenty-foot tall giants to avoid undergoing collapse, instead of altering its anatomy it would make more sense for the giants to composed of stronger materials. Giants with stronger bones and tissues will be able to evade the usual consequences of the square-cube law.
Twenty-tall giants will only require their bones and tissues to be approximately between three plus and four times stronger than the bones and tissues of ordinary human beings.
This is due to the area of supporting structures like bones will increase proportionally by the factor of a square. Effectively the increase in the strength of their biological materials is only linearly proportional to the increase in their size. This will adequately compensate to the cube increase in their mass due to their increase in volume.
Otherwise giants would have to become proportionally broader and wider to increase the area of their bones and other supporting structures to compensate for their increase in volume and the increase in load due to the increase in mass.
Giants made of stronger biomaterials will maintain the same proportions as ordinary humans. This doesn't change their anatomy, provided their increase in size doesn't exceed their increase in biomaterials' strengths.
Consider the illustrative case of the paranasal sinuses.
The paranasal sinuses have a wide variety of functions including lightening the weight of the head.
Incorporating large air filled spaces within a structure allows a large structure of lighter weight.
So too your giants! Most of their apparent bulk is full of air sacs. Birds take advantage of this same principle and at the same time augment their respiratory ability.
Being composed mostly of air would let your giant easily reach your desired size, while at the same time weighing about the same or even less than a normal human. The giants would probably want to stay indoors during windy days.
to the earlier question "Mega-human: What are the largest possible dimensions of a human?", my (accepted) answer was that a humanoid could feasibly be 7m (23 feet) tall, with a weight of 5 tons. Your 20 feet giant is a bit smaller than this, so no further modifications would be necessary than those I mentioned in the answer (unless I overlooked something). Mainly, this is a relatively larger heart to pump blood higher. You might also consider tapering your giant a bit towards the top, with legs relatively thicker than the arms and a relatively smaller head, compared to a human. The giant would after all not need a bigger brain than a human.