Other reviews report the same "problem", but seems to be "By Design". Digitec should replace the photos with those from Logitech, there it matches the actual behaviour. https://www.logitechg.com/en-us/products/gaming-keyboards/g513-backlit-mechanical-gaming-keyboard.html
I don't know the problem, but maybe remove the knob with the tool that came with it or carefully by hand.
If you see anything obvious, e.g. dirt that can be removed.
Otherwise have it replaced under warranty.
The pictures are often the same for the different configurations. The keyboard itself is the same, so they simply indicate the configuration in the specifications.
For the keyboards, you should stick to the title or the specifications if the title does not indicate it.