It's a V-slot cover for the ender 3 aluminium beam.
The base is really thin like .4 mm, so you can also use it like a light diffuser if printed in white or clear and a led strip is place in the slot.
The part is small, but in any slicer you can adjust the length at your will.
Print setting: .20 mm layer height
The author marked this model as their own original creation.