Godot 4.x example of how to launch multiple instances and tile them by using an editor debugger plugin to communicate with each instance

globals.gd

# res://globals.gd added as an autoload

extends Node


func _ready() -> void:
	EngineDebugger.register_message_capture("tile-instances", _on_tile_instances)
	EngineDebugger.send_message.call_deferred("tile-instances:get_id", [])


func _on_tile_instances(message:String, data:Array) -> bool:
	match message:
		"session_id":
			var info:Dictionary = data[0]
			var id = info.get("id", -1)
			var all = info.get("all", [])
			print(info)
			if all.size() > 1:
				for i in all.size():
					var other = all[i]
					if other == id:
						tile_window(i, all.size())

			return true

	return false


func tile_window(i:int, total:int) -> void:
	var window = get_window()
	var screen = window.current_screen
	var screen_rect = DisplayServer.screen_get_usable_rect(screen)
	var window_rect = window.get_visible_rect()
	printt(window_rect, screen_rect)
	match total:
		2:
			window.position.x = (screen_rect.size.x / 2 - window_rect.size.x / 2)
			window.position.y = (screen_rect.size.y / 2 - window_rect.size.y / 2)
			if i == 0:
				window.position.x -= window_rect.size.x / 2 + 16
			else:
				window.position.x += window_rect.size.x / 2 + 16
		3:
			pass
		4:
			pass

plugin.cfg

# res://addons/tile-instances/plugin.cfg

[plugin]

name="tile-instances"
description=""
author="mrcdk"
version="1.0"
script="plugin.gd"

plugin.gd

# res://addons/tile-instances/plugin.gd

@tool
extends EditorPlugin

var tile_instances = preload("res://addons/tile-instances/tile_instances.gd").new()

func _enter_tree():
		add_debugger_plugin(tile_instances)

func _exit_tree():
		remove_debugger_plugin(tile_instances)

tile_instances.gd

# res://addons/tile-instances/tile_instances.gd

@tool
extends EditorDebuggerPlugin

const PREFIX = 'tile-instances'

func _has_capture(prefix:String) -> bool:
	return prefix == PREFIX

func _capture(message:String, data:Array, session_id:int) -> bool:
	match message:
		"%s:get_id" % PREFIX:
			var all = []
			var sessions = get_sessions()
			for i in sessions.size():
				var session = sessions[i]
				if session.is_active():
					all.push_back(i)

			get_session(session_id).send_message("%s:session_id" % PREFIX, [{"id": session_id, "all": all}])
			return true

	return false