In PCB Layout, there's an icon in the bottom right corner of the LAYERS dialog, that allows you to adjust the contrast level when viewing multiple layers in Contrast mode.
This icon is mentioned briefly on page 41 of the (2/07/2022) tutorial. The only explanation is "– contrast level setup" This is ...

I had the same problem when working through the tutorial, using DipTrace under Windoze 7 pro.
When you mouse over a component, if it turns blue you can drag it.
If only custom components are used, sometimes this works. At other times, you mouse over the component and it never turns blue, so you can ...