Hi Christian,
When I enable them in Qimage under Color Management\Images, original JPEGs with embedded sRGB look horrible (double profiled?) whilst raws seem not affected as well as jpegs coming from another photo editor.
The camera profiles are for raw files only and should not be enabled in the images section of the CM dialogue. For jpegs with exif data, "Honour Exif ..." should be sufficient and if the profile is embedded, QU will read that. With the CM dialogue open, click F1 for the relevant help
For RAW, make sure "Enable Custom Profiles" is ticked.
You can check what QU is using as the image profile from the Exif Hot bar at the bottom of the main screen, it's shown at the right hand end.
Also, hover your mouse over thumb, right click and select "Display Image Info". That will tell you if there's an embedded profile or not - make sure the mouse is over the thumb in question.
Terry