One of the issues here is that the bone is trying to reach the IK target with its tail, but it can’t do that in its rest pose. This leads to maximum extension of the leg even when you think that shouldn’t be happening.
To fix that, enter edit mode. Snap cursor to the head of the IK target. Select the tail of the calf bone. Snap selection to cursor.
The other thing here is that it looks like you built the leg bones with a completely straight leg. That’s not really how Blender’s IK is built to function. It works very well, very easily, provided you have built a bend into the leg. (And doing that is good from a modelling/animation perspective anyways.)
It would be easier to see if this was the case if your thigh bone extended all the way to the head of the calf bone, and doing that wouldn’t affect deformation or the IK, so I’d recommend that-- again, just using snapping, snap the tail of the thigh to the head of the calf.
If you do have a straight leg, you can probably fix it really easily just by moving the head of the calf slightly toward the front of the model or the head of the thigh slightly toward the back of the model (in edit mode.)
Finally, just be aware of your IK limits, on properties/bone/IK. Once you have an appropriate bend, you should be fine without using any limits whatsoever.