Improve black prints on a colour laser printer

My Kyocera FS-C5400DN colour laser printer prints some documents that include graphics (greytone or coloured) blured

A pure textpage is perfect and most time colourpages are fine too. It looks if black would be overprinted with CMY and CMY would not have some offset.

Are there known settings in cups, or in a hidden printer menu that would improve this?
Do the files need a kind of preparation to tell the printer about colour ranges?

Here is a screenshot of the first cups configuration menu. I do not know what Trapping and Halftone will exactly do. But i guess halftone will reduce the number of different colours.
Will Trapping help?

Check in the advanced printer settings for something like “Always use black ink (toner) when printing black in color mode.”

If the setting is unchecked, it will combine CMY to create Black if printing in color mode.

I don’t know if XEROX Laser printers have this setting. I used to use a XEROX solid ink inkjet printer and I remember this setting for that printer.

The symptoms sound like a print alignment issue between black and the colors. Grey could be affected because colored dots are often used in grey gradients. See if the printer has an alignment test.