Designed minimalistic cable channel to 3D print.
These 20cm strips fit into each other from all sides. They can be put next to each other and/or form a single straight line. There are two holes for screws, but in my case I've glued these plastic stripes onto the surface. The cable it self is simply pushed into the dent which is exact size so that it holds pretty tight. Printed with PETG, which should be UV resistant and outdoors appropriate.
Now it's there on the balcony, facing south => sun. Next months and years will show how good it is.
3D design source files:
Reddit post → got a feedback → "FYI white cables are normally not UV resistant." and well these aren't indeed.