Investigate AMD GPU I2C device issues in Linux
The AMD kernel driver (amdgpu) does not expose all of the I2C buses on the GPU chip to userspace (/dev/i2c-X). It only exposes those linked to a display connector for EDID use. Unfortunately, the RGB chips are almost always attached to one of the otherwise unused I2C buses.
This issue will need to be addressed in the kernel, not in OpenRGB, but I'm opening an issue to track this issue and possibly develop a proper kernel patch to expose these buses.