Remade Main class and created Proxy interface and implementation.

src/main/java/dev/micle/xptools/proxy/IProxy.java

@@ -0,0 +1,11 @@
+package dev.micle.xptools.proxy;
+
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.level.Level;
+
+public interface IProxy {
+    MinecraftServer getServer();
+    Player getClientPlayer();
+    Level getClientLevel();
+}

src/main/java/dev/micle/xptools/proxy/Proxy.java

@@ -0,0 +1,97 @@
+package dev.micle.xptools.proxy;
+
+import dev.micle.xptools.XpTools;
+import net.minecraft.client.Minecraft;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.level.Level;
+import net.minecraftforge.common.MinecraftForge;
+import net.minecraftforge.event.AddReloadListenerEvent;
+import net.minecraftforge.event.server.ServerStartedEvent;
+import net.minecraftforge.event.server.ServerStoppingEvent;
+import net.minecraftforge.eventbus.api.IEventBus;
+import net.minecraftforge.fml.event.lifecycle.*;
+
+public class Proxy implements IProxy {
+    private static MinecraftServer server = null;
+
+    // Common setup
+    public Proxy() {
+        // Register mod event bus listeners
+        IEventBus modEventBus = XpTools.getFMLJavaModLoadingContext().getModEventBus();
+        modEventBus.addListener(Proxy::setup);
+        modEventBus.addListener(Proxy::imcEnqueue);
+        modEventBus.addListener(Proxy::imcProcess);
+
+        // Register event bus listeners
+        MinecraftForge.EVENT_BUS.addListener(Proxy::onAddReloadListeners);
+        MinecraftForge.EVENT_BUS.addListener(Proxy::serverStarted);
+        MinecraftForge.EVENT_BUS.addListener(Proxy::serverStopping);
+    }
+
+    private static void setup(FMLCommonSetupEvent event) {}
+
+    private static void imcEnqueue(InterModEnqueueEvent event) {}
+
+    private static void imcProcess(InterModProcessEvent event) {}
+
+    private static void onAddReloadListeners(AddReloadListenerEvent event) {}
+
+    private static void serverStarted(ServerStartedEvent event) {
+        server = event.getServer();
+    }
+
+    private static void serverStopping(ServerStoppingEvent event) {
+        server = null;
+    }
+
+    @Override
+    public MinecraftServer getServer() {
+        return server;
+    }
+
+    @Override
+    public Player getClientPlayer() {
+        return null;
+    }
+
+    @Override
+    public Level getClientLevel() {
+        return null;
+    }
+
+    // Client setup
+    public static class Client extends Proxy {
+        public Client() {
+            // Register mod event bus listeners
+            IEventBus modEventBus = XpTools.getFMLJavaModLoadingContext().getModEventBus();
+            modEventBus.addListener(Client::setup);
+            modEventBus.addListener(Client::postSetup);
+        }
+
+        private static void setup(FMLClientSetupEvent event) {}
+
+        private static void postSetup(FMLLoadCompleteEvent event) {}
+
+        @Override
+        public Player getClientPlayer() {
+            return Minecraft.getInstance().player;
+        }
+
+        @Override
+        public Level getClientLevel() {
+            return Minecraft.getInstance().level;
+        }
+    }
+
+    // Server setup
+    public static class Server extends Proxy {
+        public Server() {
+            // Register mod event bus listeners
+            IEventBus modEventBus = XpTools.getFMLJavaModLoadingContext().getModEventBus();
+            modEventBus.addListener(Server::setup);
+        }
+
+        private static void setup(FMLDedicatedServerSetupEvent event) {}
+    }
+}