The above variation of the impossible triangle was created in 1934 by the Swedish graphic artist Oscar Reutersvärd. Much of his work explored the idea of impossible three-dimensional geometry, earning him the title of the “father of the impossible figure”.

It is impossible to arrange a set of cubes in the looping triangular way above, as each side of the triangle of cubes appears to be both in front of and behind the opposite corner.

https://www.illusionsindex.org/i/impossible-triangle

https://im-possible.info/english/articles/triangle/triangle.html