Hi and welcome
If you are a c4doctane user, you need to click-select one of the categories, by expanding the black arrow to start to load and see the material preview icons.
Please, also note that you need to access and download LiveDB materials from an already saved scene, so the textures can be correctly saved in the “tex” folder of the scene.
If you are not a c4doctane user, pleaser post a screenshot, thanks.
ciao Beppe