After searching for a showerhead holder to 3D print and not finding anything that matched the aesthetics I was looking for, I decided to design my own. This is what I came up with:

In the files, you will find variations of the “Showerhead adapter” STL to fit 18, 20, 22 and 25mm rods. Print the size that matches what you have at home. Print this part with normal supports with 30-degree threshold angle. I had some failed prints when I printed with less than that or with Tree supports. This file prints two parts that go together, when you remove the supports you should end up with 2 parts like in the picture below:

On the print profile, you will find four plates with the best print setup I found, each for a specific variant.

Print the one that fits your shower setup:

Plate 1: 25mm

Plate 2: 22mm

Plate 3: 20mm

Plate 4: 18mm

The pieces simply screw together, just like a regular showerhead holder. The piece highlighted in the render below serves to apply friction to the shower rod.

If your showerhead fits a bit loose, I recommend gluing a piece of waterproof rubber tape on the inside. I didn't need it in mine and I am using it without issues.

Happy showering!