This video shows my first iteration of a 3D printed strain wave gear:

It had some disadvantages:

The sliding surfaces were milled out of aluminium that worked fine, but my goal is to have a design that was only printed and assembled without additional labor.

The ball bearing on the wave generator was to small and caused to much wear and tear on the flex spline

The shaft coupling bent the wave generator, resulting in unwanted backlash due to too much play.