This object would be simple to make with an electromagnetic sheet metal brake. Magnabend is a name from many years ago (possibly the name of the original invention?); there are now several vendors selling similar machines. In this machine the clamping bar is held with magnetism rather than mechanical force. This allows varying lengths of clamp bar and allows the clamp bar to be open at the ends.
Many of the vendors' offerings are priced approaching $3000, but maybe seeing how the part could be made with a magnetic brake will give you ideas how you might create a special tool around the corner of a welding table, in a vise or hydraulic press, etc.
A Z shape comprising the reverse bend and the regular bend opposite would be made in the normal way. Then, for folding the other two sides, the Z shape would be laid on the brake with the downward-facing flap off one end of the brake. A clamp bar would be laid inside, the magnet is energized and the fold is made, and then everything is reversed to the other end of the brake to do the second side.
In this illustration the 1/2" steel clamp bar is laid on top of the part. The rectangle on the front face of the machine is the bending leaf. The hinges are recessed in the back side of that leaf so that it pivots around a point somewhere in the gap between the machine body and the bending leaf -- roughly around the upper rear corner of the bending leaf.