It seems like adjusting the SDR brightness also changes the HDR peak brightness, is that normal?
Yes, as of Plasma 6.3, this is considered intended behaviour, 499934 – Plasma 6.3 broke HDR brightness
Will they change it in Plasma6.4?
In Plasma 6.4, the “Maximum SDR brightness” setting will be moved out of the monitor settings form in Display Configuration, instead it can be set by an HDR calibration tool. It’s not meant to be a general brightness setting but rather a tweak for graphics professionals who work with HDR.
The “Brightness” setting in the Display Configuration settings page will remain, and does not affect the brightness of HDR content in any way. This “Brightness” setting is also the same that the “Brightness and Color” applet provides through the system tray. It will change overall brightness when HDR is disabled (using the display/monitor backlight if possible) and will change brightness of just SDR content when HDR is enabled.
It’s just a setting to configure “100% brightness”. Everyone gets to set it to what makes sense for themselves / the display when configuring the display.
It does adjust HDR content. There’s nothing special about HDR content that would make it somehow inherently always have the perfect brightness. It needs a brightness slider the exact same as all other content.
Sigh, and thanks for the corrections. I’m going to stop commenting on HDR-related conversations because it looks like I know much less than I thought I did.