Nice and simple - a case for your Mk. 1 Stream Deck for use with @RostaP's multifunction arm system.
Printing
Print one of each.
stream deck case: Place this on its bottom. No supports are needed here. After printing, tap the four holes on the top for M3 (you may be able to self-tap these with screws).
stream deck lid: Place this on its top - use a bottom layer pattern you like. Just clean out the bridged M3 counterbores.
stream deck case padding: This goes between your Stream Deck and the case. Print this in your favorite flexible filament. I recommend that only your first layer is solid, and use a sparse gyroid infill to give a bit of cushioning inside. No perimeters, no solid top layers. If you don't have a flexible filament, you may be able to get away with only printing the main section in a solid filament.