Notwithstanding that the metal sheet thickness may not remain the same when bent, here is a simple-minded approach.
Basically do a cross section outline of the bend and Extrude. Then Transform/Rotate a copy 90 degrees and then Translate one top corner point to the other. Extrude to complete.
I exaggerated the bend for clarity.
Notice that the cutout is a 1/4 ogive (bullet shape). So a simpler way would be to Shell out your box and Subtract the 1/4 ogive from each corner. Create the ogive with a cross section and the Revolve tool. Once you determine the dimension for each thickness of sheet metal this would be very easy to do for a given corner cutout. You will have to trade off the radius of the bend with the fold up gap.
If your bend is not circular (the metal stretches at top and compresses at bottom), it gets more complicated and if you try to bend too sharply, the metal will usually crack.
I once worked in a sheet metal stamping plant a long time ago. Can still hear the kerplunk of the presses.
Hope this helps.
Thank you for your answer, the thing is that if we draw it like you did, the end product is going to look like this.
But i want it to look like this
From the picture, it looks like the metal is first being deformed downward and stretched resulting in the thinner section at the top.
How to draw? Not clear… perhaps take a photo at a right angle, import and then use this to develop the cross section. Lots of examples in the tutorials.