Is there a way to dim the main screen? I have been through all options. And the deal on the left of steering wheel only dims the buttons.

 

There should be an option in the center screen menus.

If you go to Setup -> Display, you can adjust. If you have Lexus Display Audio, you would just hit the Menu button, and then Display.

Here's how it looks in my Nav-equipped car (I believe 2017+ are similar if not identical).

 

So it gives me an option for auto screen change from blue to black background at night but not a dimmer….

 

The "Day Mode" shown is photo 2 of Post #2 may be the culprit.
It only appears in the settings menu when the sensor thinks it is dark.
Day Mode causes the main screen to be Day time bright even at night
Cover the dark dime sized dome on the dash near the defroster vents
with an opaque object such as a cell phone and wait 20 seconds for the
screens to darken. Now open the Settings and turn off the Day Mode.

 

I can adjust the brightness regardless of whether the Day Mode is on or not. It was off in my screenshot because I was in my garage when taking the photos. I don't know whether the thread author has that.

Even if it is there, one can still adjust the brightness.

 

Maybe it's different on the pre-refresh models. Does your setup look more like the one in this video?