Golden carrots do not appear in the creative mode foodstuffs menu.

Duplicates MC-67566 which works as intended, though I think adding it to both Brewing and Foodstuffs would make more sense.

Items can currently only have one category in the creative menu.

Golden Carrots are in the Brewing Section due to there main use being for making potions. The eating is just a bonus of the Golden Carrot (Like how Dried Kelp can make a Dried Kelp Block). This is how it is intended to be.

NeunEinser, not really since the fix of MC-107550. e.g. Unbreaking Ⅲ appears in both Tools and Combat category.

Enchanted books have special treatment in the code. Usually Items are registered like this:

STONE = register(Blocks.STONE, ItemGroup.BUILDING_BLOCKS);
The ItemGroup only accepts one argument.

An enchanted book is a special item. There is only one item id for it, enchantments are NBT data. So in that registry, enchanted books only appear once with no category.

There is special code for adding enchantments to categories:

TOOLS = (new ItemGroup(8, "tools") {
            public ItemStack createIcon() {
                return new ItemStack(Items.IRON_AXE);
            }
        }).setEnchantments(new EnchantmentTarget[]{EnchantmentTarget.ALL, EnchantmentTarget.DIGGER, EnchantmentTarget.FISHING_ROD, EnchantmentTarget.BREAKABLE});

Oh I get it, thanks for your explanation. (Mojira should provide a feature to add reactions to a comment so I can just add a thumb up to your comment without updating this ticket 😛 emm, seems that I treat here as a discussion area, my bad)