CMYK is a printing color, which is mainly used for printing, and its color gamut is smaller than RGB, so when converting RGB color into CMYK, we should pay attention to the color of the picture.
X-display stands, large outdoor, photo shooting, etc. are printed by large inkjet printers. In fact, they are an enlarged printer with the same properties as the printer printed by your printer. If RGB is used, the color will be brighter. Of course, you can also make them in CMYK, just as your printer can print RGB and CMYK.
Printing uses CMYK colors, that is, four colors. Similarly, when printing, four colors of blue, red, yellow and black are printed on paper four times. Since it is printed four times, there will be errors if the printing machine is poor. For example, if your text color is a mixture of two colors, then the two colors will not completely overlap, so it will look like a ghost.
The principle of printing is that the nozzle of the printer sprays all colors on the paper at once, so there are few colors that overlap badly. Of course, this situation does not rule out the possibility of an old printer. This can also happen if the large inkjet printer is used for a long time, obsolete or the nozzle is not calibrated.