Do you know, that… ?

During convert a solid to a sheet metal you must select a fixed face and the edges to be flanged. The matter becomes a bit more complicated in the situation, when there is a lot of edge.

Therefore, you can advance in the model insert fillets, to select during conversion Collect All Bends! Of course, we use automatic edge selection.

Just remember in a similar situation, that one edge must be removed, for a break.