How to deal with generic numerical sensor data

I have a BME680 which reports an SIAQ score that does not fit any specific device_class listed here: so I did not specify it. This, however, leads to history graphs being displayed as a bar (with a LOT of colors …).
How do I correctly deal with this?

Add a unit_of_measurement: option to the entity’s configuration. The value can be any unit you want (real or fictitious)

  unit_of_measurement: 'bogus'