This has turned out to be more tedious than I thought. I did the usual looking up tools to use, and found they use ddci, like ddcutil and ddccontrol, but they're very slow. Before setting them up, KDE's brightness slider did software brightness, now it does hardware brightness but now takes a whole moment with each brightness, I can't smoothly slide it back and forth like I can on laptops. I have a Dell G3233Q connected via USB For USB ports and DisplayPort.