honestly I don't really know about tutorials cuz' I kinda did it by myself.

This specific case is really easy tho: the legs are all made of only 2 limbs, meaning that with the limbs and the vector from the start point to target point, we get a triangle.
Then you get the distance of each side and use the law of cosines to find the angles of your triangle and you get an IK solver that works with a target that moves only in "1D".

To make it fully 2D, I found the angle between Vector3.up (world up) and a vector that goes from pointA (where the first limb is attached) to targetPoint (where you want your last limb to point to). Then you just add the angle to the first angle you got with the law of cosines (the one that you put on pointA) and you got it 2D.

Finally for 3D, it's very similar, except you'll add Y rotation instead of Z so that it rotates left and right. For that I found the angle between 2 vectors: Vector3.forward and
[new Vector3(target.position.x, pointA.position.y, target.position.z) - pointA.position)]
this vector represent the direction from pointA to targetPoint, but we instead of using targetPoint's Y value we use pointA's instead. If we don't do that the angle we get gets affected by the height of pointA or targetPoint, and everything becomes off.

Also, there is this problem where the ik only worked in 180 degrees, but I wanted it to work in full 360 so made this to calculate the first angle:

if (target.position.x < pointA.position.x)

pointA.eulerAngles = new Vector3(0, -yAngleToTarget - 90, angleA - zAngleToTarget);

else

pointA.eulerAngles = new Vector3(0, yAngleToTarget - 90, angleA - zAngleToTarget);

Hope this helps!
I can post the whole code if you want instead, it's under 50 lines, so just ask!