Solved Player can’t drop the item from the creative

My problem:
When I right-click, I am given a creative. I press "E" to enter the inventory and I can take things from the creative to my inventory, BUT I cannot hover over the item and click "Q" to throw it away, nothing happens. Wish the items were thrown away.

Code:

package plugin.grenka.plugin;

import org.bukkit.GameMode;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.Action;
import org.bukkit.event.player.*;
import org.bukkit.inventory.ItemStack;
import org.bukkit.plugin.java.JavaPlugin;


import static java.lang.Thread.sleep;

public final class Plugin extends JavaPlugin implements Listener {
    boolean ibb = true;



    @Override
    public void onEnable() {
        // Plugin startup logic
        System.out.println("The plugin is starting up.");
        getServer().getPluginManager().registerEvents(this, this);

    }
    @EventHandler
    public void onPlayer(PlayerInteractEvent event) throws InterruptedException {
        Player player = event.getPlayer();
        Action action = event.getAction();

        if (action.equals(Action.RIGHT_CLICK_AIR) || action.equals(Action.RIGHT_CLICK_BLOCK)) {
            if (player.getItemInHand().getType() == Material.TRIDENT) {
                player.getInventory().getItemInMainHand().setAmount(player.getInventory().getItemInMainHand().getAmount() - 1);
                player.updateInventory();
                player.setGameMode(GameMode.CREATIVE);
                sleep(2000);
                player.setGameMode(GameMode.SURVIVAL);



            }
        }
    }


    @EventHandler
    public void PlayerAdvancementDone(PlayerAdvancementDoneEvent event){
        Player player = event.getPlayer();
        player.getInventory().addItem(new ItemStack(Material.TRIDENT, 1));
    }
}

If I turn on the creative myself, then that's okay, if the plugin turns it on, I can't. And all what i do in creative - everything rolls back. I think problem with "sleep"...

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

I change to

Code:

Bukkit.getScheduler().runTaskLater(this, () -> {
                    player.setGameMode(GameMode.SURVIVAL);
                }, 40L);