Older models (2014-) have a Vacuum Fluorescent (VF) dot matrix display in the center of the cluster. While the brightness of this display can be altered by turning on/off the headlights, using the dimmer switch, etc. you should know that all VF displays simply lose brightness over time. Thus, they get dimmer as they get older. The only solution for that is to replace the display.
But, if you don't mind taking your cluster apart, there is often what appears to be a dark green "window tint" like filter installed over these displays. Depending on the design of the cluster, it may be removable. If you can get this filter to come out, the display should be quite a bit brighter. Don't know if any of this helps, sorry!