I had no expectations but I was hoping that the category item icons would be shown in book details, so I gave it a spin.
After adding a category item icon, it wasn't obvious to me how I could remove it; so, I used brute force and deleted it from tb_icons, when that didn't make it go away I guessed it was cached so I restarted calibre… et voilà, gone completely:
I now know that the way to remove a category item icon is to select the Manage icon for <item name>->Use the default icon for <item name> option, viz:
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But seeing that icon free "Banking" leads me to ask: Would it be possible to provide an option that hid all icons in the Tab browser apart from the top level category icons? For me they are distracting space wasting clutter.
BR