Monitors used to have easy rotary buttons to adjust brightness and contrast. Though I don’t remember it actually being necessary that often. Of course, the monitors rarely changed location.

In assuming you are not using your keyboard to set brightness because it’s an external display plugged into a laptop? Search for a DDC application for your desktop, it’s amazing, the brightness controls of your laptop will then control the external display as well. I use lunar on my MacBook, it was a revelation.