Use the Unfold feature to pick the bends that you want to flatten. It is not necessary to flatten the model completely. It is possible to add the linear hole pattern. For this exercise, with the model unrolled in its current state, you will first unfold an additional two 90-degree bends.
As soon as you select the face shown, the bends that can be unfolded relative to that face highlight:
Once the bend is selected, the part previews in the unfolded state.
Next, you finish creating the Unfold feature.