I cannot claim any real experience with either TKD nor boxing. I pretty much get what you are describing, but I donāt think I can comment much.
Here is the thing: if you initiate a turn from the upper body, from the hips or waist or shoulders, then that point upwards will move first and there will be a delay, even if very brief, before the feet pivot. That delay causes a twisting pressure on the knees as the feet are dragged into place which, over time, can lead to injury. Itās the kind of thing that can take years and you donāt realize the damage is being done until suddenly one day you are in pain. It didnāt happen overnight, it was a long time in the works, although one slightly traumatic event might be what finally pushes you over the line.
If you focus on rotating the feet and initiating the turn from the feet, you can then turn both the lower leg and the upper leg together as a unit, and eliminate that rotational pressure on the knee. It is near impossible to adequately describe in words and needs to be demonstrated in Person to teach the method, but it involves pressing the feet against the ground to push and drive the rotation. But the feet cannot be left behind to be later dragged into place after the rotation has been done. Doing so will put bad pressure back on the knees, as well as the ankles. So the feet push and rotate, allowing the full leg to rotate as a unit, driving the hips and torso into the rotation. There is no twisting of the spine. It is a specific methodology to teach this and it requires systematic training to develop it. Not the kind of thing that you can just play with a bit and figure it out.