I wasn't pleased with the designs I found and tried on Thingiverse for a mudguard bracket for the Xiaomi M365 scooter. I Think they were overly complex and weak.
This design is much simpler and stronger because it's still thick enough to be robust but also elastic enough to handle vibrations you can get from the ground / speed bumps / pavement.
Print with an Wall Thickness of 2mm (Shell settings).
This will make the section of the bracket without infill, which will make the part stronger with efforts applied only in the right direction. (Cura pictures shows that)
The bigger part will still have Infill, user a standard value for this.
For the build plate adhesion, maybe try to use a Brim to hold better.
I used supports but maybe that's not really needed. There isn't much anyway.
The bracket is attached to the rear of the original mudguard with the 2 original screws.
It's also using the 2 big screws from the wheel axle. I only kept the 2 big washers to prevent the part to be crushed when screwing the 2 big screws.
It's using a oblong hole for easier adjustments.