Why isn't my item popping up in the creative inventory?

I’m trying to create an item. In RP/textures/items, I have its texture. I defined the texture in RP/textures/item_texture.json. In BP/items I defined its behaviors. I kept all these in the development_resource_packs and development_behaviour_packs folder respectively. When I load the game, it doesn’t show the items in the creative inventory. It is something like an enchanted egg. I also made other enchanted eggs like turtle and dragon, but all of these never showed up. But all the recipes in BP/recipes are working fine (Except for the recipes for the enchanted eggs)

Here’s the texture:

item_texture.json:

{
    "resource_pack_name": "Minecraft++",
    "texture_name": "atlas.items",
    "texture_data": {
        "egg": {
            "textures": [
                "textures/items/egg"
            ]
        },
        "diamond": {
            "textures": [
                "textures/items/diamond"
            ]
        },
        "turtle_egg": {
            "textures": [
                "textures/items/turtle_egg"
            ]
        },
        "dragon_egg": {
            "textures": [
                "textures/items/dragon_egg"
            ]
        }
    }
}

soul_egg.json:

{
    "format_version": "1.16.100",
    "minecraft:item": {
        "description": {
            "identifier": "mpp:soul_egg",
            "category": "nature",
            "is_experimental": false
        },
        "components": {
            "minecraft:max_stack_size": 64,
            "minecraft:stacked_by_data": true,
            "minecraft:foil": true,
            "minecraft:icon": {
                "texture": "egg"
            },
            "minecraft:display_name": {
                "value": "item.mpp:soul_egg.name"
            },
            "minecraft:hover_text_color": "aqua"
        },
    }
}

Edit:
I changed the value under minecraft:display_name, because I added it to en_US.lang file