Hello Dari21

Since the question is not 100% clear, I will give 2 answers:
(1) In the printer driver on the PC and on the device (e.g. copy function), I can select whether I want to print in colour or B/W (monochrome/mono). The default setting in the printer driver of the PC is "Auto" = the driver/device selects whether the colour toners (CMY) are used or not based on the document content. This is to save (colour) toner.
If you manually select "monochrome" (=only BK toner is used) to print/copy only B/W, you can still print even though one or more colour toners are used up.
However, the used colour toners must still be/remain in use, otherwise b/w printing will not work.
(2) You can still scan with the machine even if one (e.g. magenta) or all toners are displayed as "Replace toner" = used up. Again, all toners must still be in the machine.
Greetings