Instead of spending 18.20€ on the original support, which would probably break a second time because the plastic is really low quality, I decided to make my own replacement for the broken piece.

You should print it lying over the axis as in the fifth picture. I used a layer height of 0.16mm (although 0.28mm also worked on the initial prototype, it was just a bit rougher), infill of 40%, low density supports, with a Z Distance of 0.4mm and material PETG. The PLA prototype also worked well, but the shower temperatures would probably melt it gradually, so I'd recommend either PETG or ABS. I prefer PETG since it can be fully recycled and doesn't release so many toxic fumes as ABS while printing, a PETG spool is definitely a better investment than the original shower arm.

To install it, you should remove the original plastic piece (I used a scraper and a hammer to dig into the articulation breaking the axle), print this and insert it with the narrower part of the hanging hole pointing down. Inserting it might require some strength, I was using an allen key as a lever.

It works as the original piece and can be easily articulated, I intentionally made the adjustment a bit less clicky than the original by slightly reducing the radius.

EDIT: After 4 month of daily use and adjustment (everyone in the house likes the angle different), I can confirm it still survives with no issues.