The way to solve this for me is to ONLY use the number boxes instead of the slider to change the color values using the virtual Steam keyboard, then press the Enter button. However, you can only do this once before it locks you out and I wouldn't touch the slider at all or it breaks. You have to completely back out of the advanced controller settings, then go back in to do the same thing for the brightness and then yet again for the saturation. It's very janky and inconvenient, but it probably has to do with the new slider UI or the way the settings apply to the controller inside the "Steam\steamapps\common\Steam Controller Configs\preferences_[ControllerMacID]" file (you can edit the controller config inside here too). It's weird that this works once, but locks up, so it should be able to be fixed since it did work before somehow. Also turning off your controller after editing the LEDs might work, but it doesn't really work for me. I think there's an issue with the UI code to change the LEDs that Valve would need to fix.

Thanks for the advice, managed to fix my DS4v2 by changing the led color, saturation and brightness one value at a time using the onscreen keyboard.

Fedora Linux 43 (Workstation Edition) (64 bit)
Kernelversion: 6.17.10-300.fc43.x86_64
X-serverleverantör: The X.Org Foundation
X-serverversion: 12401009
X Window Manager: GNOME Shell
Version av Steam Runtime: steam-runtime_1.0.20251111.181377
Klientinformation:
Version: 1764630020