Okular doesn't print in grayscale

I want to print in grayscale a pdf document with colored parts.
So I go to “Print”, select the printer property button and set the grayscale mode.
But Okular prints always in color mode.

No problems with other apps (LibreOffice for example).

OS: KDE Neon; printer: Brother MFC-J880DW

I have the opposite problem, i want to print in colour mode, but my HP Envy 5540 print in grey scale only.
Other Apps like LibreOffice are ok and print in color mode.
Actually, in the past, I changed from colour mode to grey, due to run out of the colour cartridge.
But now I cannot reverse this setting.
Does someone know where is written this information ?
(Okular ver. 24.12.1; KDE Neon 6.2)