Any of the 3 piece cube units with flat ends can be used to make a mobius triangle. Complete the unit as per @ivan-g original post on the diamond window cube by Lewis Simon the unit should have a diagonal line through the body and the end flaps folded behind in triangles.
Fold three units.
Construction:
Insert the red and blue units into the purple unit as shown.
Turn the model over carefully holding all three units in place.
Bring the blue unit across and tuck the purple unit in where my thumb is (second panel across).
Repeat with the red unit.
Let the two arms naturally curl towards each other and insert the blue unit into the third panel of the red unit.
Tuck the last red unit into the third panel on the blue unit.
The last unit can be hard to insert.
Happy folding, Grace.