final LinkedHashMap.Entry<K,V> nextNode() {
    LinkedHashMap.Entry<K,V> e = next;
    if (modCount != expectedModCount)
        throw new ConcurrentModificationException(); // right here
    if (e == null)
        throw new NoSuchElementException();
    current = e;
    next = e.after;
    return e;
}

public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTask> implements CommandSource, AutoCloseable {

    public final Map<ResourceKey<Level>, ServerLevel> levels;

    public MinecraftServer(...){
        this.levels = Maps.newLinkedHashMap();
    }

    public void tickChildren(BooleanSupplier booleansupplier) {
        ...
        Iterator iterator = this.getAllLevels().iterator();
        ...
        
        while(iterator.hasNext()) {
            ...
            Activate command blocks
            ...
        }
    }
}

public final class CraftServer implements Server {
    public World createWorld(WorldCreator creator) {
        // Lots of code... 
        this.console.initWorld(internal, worlddata, worlddata, worlddata.worldGenSettings());
        internal.setSpawnSettings(true, true);
        this.console.levels.put(internal.dimension(), internal); // right here
        this.getServer().prepareLevels(internal.getChunkSource().chunkMap.progressListener, internal);
        // Some more code...
    }

    public boolean unloadWorld(World world, boolean save) {
        // Lots of code...
        this.worlds.remove(world.getName().toLowerCase(Locale.ENGLISH));
        this.console.levels.remove(handle.dimension()); // right here
        return true;
    }
}

// do everything else
if(!worldsAreBeingTicked){
    Modify MinecraftServer.levels now because it is safe
} else {
    Add world to list so it can be loaded/unload later
}

package dev.benergy10.testplugin;

import org.bukkit.World;
import org.bukkit.WorldCreator;
import org.bukkit.WorldType;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.plugin.java.JavaPlugin;

public final class TestPlugin extends JavaPlugin {

    @Override
    public void onEnable() {
        // Plugin startup logic
        getCommand("testloadworld").setExecutor(this);
    }

    @Override
    public void onDisable() {
        // Plugin shutdown logic
    }

    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if (args.length != 1)
            return false;

        String choice = args[0];
        switch (choice) {
            case "create" -> {
                World world = WorldCreator.name("testworld")
                        .environment(World.Environment.NORMAL)
                        .type(WorldType.NORMAL)
                        .createWorld();

                getLogger().info(String.valueOf(world));
                return true;
            }
            case "delete" -> {
                boolean result = getServer().unloadWorld("testworld", true);
                getLogger().info(result ? "Deleted successfully" : "Deleting failed");
                return result;
            }
            default -> {
                return false;
            }
        }
    }
}

name: TestPlugin
version: ${project.version}
main: dev.benergy10.testplugin.TestPlugin
api-version: 1.19
commands: 
  testloadworld: 
    description: Testing world load

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>dev.benergy10</groupId>
    <artifactId>TestPlugin</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>TestPlugin</name>

    <properties>
        <java.version>1.8</java.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>14</source>
                    <target>14</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.2.4</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <createDependencyReducedPom>false</createDependencyReducedPom>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

    <repositories>
        <repository>
            <id>spigot-repo</id>
            <url>https://hub.spigotmc.org/nexus/content/repositories/snapshots/</url>
        </repository>
    </repositories>

    <dependencies>
        <dependency>
            <groupId>org.spigotmc</groupId>
            <artifactId>spigot-api</artifactId>
            <version>1.19-R0.1-SNAPSHOT</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
</project>

    @Override
    public boolean onCommand(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, @NotNull String[] args) {
        if (args.length != 1)
            return false;

        String choice = args[0];
        switch (choice) {
            case "create" -> {
                World world = WorldCreator.name("testworld")
                        .environment(World.Environment.NORMAL)
                        .type(WorldType.NORMAL)
                        .createWorld();

                getLogger().info(String.valueOf(world));
                return true;
            }
            case "delete" -> {
                boolean result = getServer().unloadWorld("testworld", true);
                getLogger().info(result ? "Deleted successfully" : "Deleting failed");
                return result;
            }
            default -> {
                return false;
            }
        }
    }