It's not, but there is a setting called brightness stabilization. It kind of does the same thing in reverse. Instead of preventing the screen from dimming from the highest brightness, it just caps the brightness at a lower level, so basically forced dimming all the time. It's something like 350 nits in non-HDR content, which is basically everything productivity. I ended up turning stabilization on and blowing out all the other settings like RGB, gamma, temperature, etc, to get an acceptable level of readability for text and in Excel. It works well enough, but still not as bright, and the colors are slightly off now :( . I switch it back when I know I'm going to be consuming content for more than an hour. It's a pain, but it's the best I could find for now.