This part replaces the top part of a mudguard holder on some models of Gazelle (children) bikes. I hope this helps for someone.
This is only the upper part. The part most likely to break. Included is the Fusion360 archive to help you get started if you need the base as well (black part in pictures).
Technical detail summary, see technical drawing for details:
Update: added step file.
p.s. I am curious if anyone used this part, please leave a comment.
The author marked this model as their own original creation.