I've posted this on one of the other many threads on this subject but here goes again.
It's clearly a bug, Jeep needs to fix it. But I've worked out how to adjust the brightness:
In manual brightness mode and with the headlight set to Auto I've found that:
When the headlights are automatically switched on, I can adjust the brightness setting for when the headlights are off.
When the headlights are automatically switched off, I then have access to the headlights-on brightness setting.
So you can adjust the brightness level setting for the opposite of the state of the headlights.
Doesn't seem to apply if you manually switch the headlights on or off.
Dumb, but at least it gives the ability to set the brightness manually for those struggling to see their display.