EditarItemInPacote.java

        ProtocolManager manager = ProtocolLibrary.getProtocolManager();

        manager.addPacketListener(new PacketAdapter(Bukkit.getPluginManager().getPlugin("WLib"), PacketType.fromClass(PacketPlayOutSetSlot.class), PacketType.fromClass(PacketPlayOutEntityMetadata.class), PacketType.fromClass(PacketPlayOutEntityEquipment.class)) {

            @SneakyThrows
            @Override
            public void onPacketSending(PacketEvent event) {
                final Object handle = event.getPacket().getHandle();
                if (handle instanceof PacketPlayOutSetSlot)
                    setSlot((PacketPlayOutSetSlot) handle);
                if (handle instanceof PacketPlayOutEntityMetadata)
                    entityMetadata(event.getPacket(), (PacketPlayOutEntityMetadata) handle);
                if (handle instanceof PacketPlayOutEntityEquipment)
                    entityEquipment((PacketPlayOutEntityEquipment) handle);
            }

            private boolean isValidItem(ItemStack itemStack) {
                final net.minecraft.server.v1_16_R3.ItemStack copy = CraftItemStack.asNMSCopy(itemStack);
                return copy.hasTag() && copy.getTag().hasKey("WLib-glowing");
            }

            private ItemStack fixItem(ItemStack itemStack) {
                final ItemMeta itemMeta = itemStack.getItemMeta();
                itemMeta.addEnchant(Enchantment.ARROW_INFINITE, 1, true);
                itemMeta.addItemFlags(ItemFlag.HIDE_ENCHANTS);
                itemStack.setItemMeta(itemMeta);
                return itemStack;
            }

            @SneakyThrows
            public void entityEquipment(PacketPlayOutEntityEquipment handle) {
                final Field field = handle.getClass().getDeclaredField("b");
                field.setAccessible(true);

                List<Pair<EquipmentSlot, net.minecraft.server.v1_16_R3.ItemStack>> items = (List<Pair<EquipmentSlot, net.minecraft.server.v1_16_R3.ItemStack>>) field.get(handle);

                for (Pair<EquipmentSlot, net.minecraft.server.v1_16_R3.ItemStack> item : items) {
                    final CraftItemStack stack = CraftItemStack.asCraftMirror(item.getSecond()).clone();
                    if (!isValidItem(stack))
                        continue;

                    final Field second = item.getClass().getDeclaredField("second");
                    second.setAccessible(true);

                    second.set(item, CraftItemStack.asNMSCopy(fixItem(stack)));
                }
            }

            @SneakyThrows
            private void entityMetadata(PacketContainer packet, PacketPlayOutEntityMetadata handle) {
                final Entity entity = packet.getEntityModifier(player.getWorld()).read(0);
                if (!(entity instanceof org.bukkit.entity.Item))
                    return;

                final ItemStack itemStack = ((org.bukkit.entity.Item) entity).getItemStack().clone();
                if (!isValidItem(itemStack))
                    return;

                final Field field = handle.getClass().getDeclaredField("b");
                field.setAccessible(true);
                List<DataWatcher.Item<?>> items = new ArrayList<>((List<DataWatcher.Item<?>>) field.get(handle));

                final DataWatcher.Item<?> item;

                int index;
                if (items.size() == 8)
                    item = items.get(index = 6).d(); //new item
                else
                    item = items.get(index = 0).d(); //item merge
                final Field itemField = item.getClass().getDeclaredField("b");
                itemField.setAccessible(true);
                itemField.set(item, CraftItemStack.asNMSCopy(fixItem(itemStack)));
                items.set(index, item);

                field.set(handle, items);
            }

            @SneakyThrows
            private void setSlot(PacketPlayOutSetSlot packet) {
                final Field field = packet.getClass().getDeclaredField("c");
                field.setAccessible(true);

                final net.minecraft.server.v1_16_R3.ItemStack stack = ((net.minecraft.server.v1_16_R3.ItemStack) field.get(packet)).cloneItemStack();
                final CraftItemStack newItemStack = CraftItemStack.asCraftMirror(stack);
                if (!isValidItem(newItemStack))
                    return;

                field.set(packet, CraftItemStack.asNMSCopy(fixItem(newItemStack)));
            }
        });

        @EventHandler
        public void onClick(InventoryClickEvent event) { //for some reason that idk, when in creative and interacting with the fake item, it makes the fake item a real item in server-side, which we dont want
            final ItemStack cursor = event.getCursor();
            if (cursor == null || cursor.getType() == Material.AIR)
                return;

            if (Item.fromItemStack(cursor).hasNbtTag("WLib-glowing")) {
                cursor.removeEnchantment(Enchantment.ARROW_INFINITE);
                final ItemMeta meta = cursor.getItemMeta();
                meta.removeItemFlags(ItemFlag.HIDE_ENCHANTS);
                cursor.setItemMeta(meta);
            }
        }