What else have you tried from that page?
Do I have to build the rpi_ws281x library in another way instead of "scons deb"?
No need to build the library. Hyperion has it built in.
What and where is the built output? Where do I have to copy it? How does Hyperion know to use it?
Again its built in. No need to bother.
The important part on that page is in this section ( https://github.com/jgarff/rpi_ws281x#limitations )
Try the suggestions in that section.
Try these steps, as it uses the SPI portion of the driver instead of the PWM portion. https://hyperion-project.org/t…rom-host.3187/#post-12230