UV maps names shouldn't be included in the material
Many people rename the UV maps and this means the materials won't work for them out of the box.
Quite often including such names also generates black thumbnails from the automatic thumbnailer in the add-on.
You can simply delete the UV map names from the material and regenerate the thumbnails.
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In this short article, we will talk about Fantasy Design. The BlenderKit team sees Fantasy Design - as a design not of a very high level. As a rule, novice designers do not have enough knowledge, but they have a great desire to do Fantasy Design.