The Blockly is doing crap - and cant be fixed in there, u have to learn micropython...i asked a friend - and he had the following solution:

import os, sys, io
import M5
from M5 import *
import m5ui
import lvgl as lv
from umqtt import MQTTClient
import time

page0 = None
page1Licht = None
button0 = None
button1 = None
Akkubar2 = None
led0 = None
led2 = None
charge = None
button2 = None
button3 = None
led3 = None
led4 = None
button4 = None
mqtt_client = None

msg = None
last_ui_update = 0   # <---- UI Timing


# ---------- MQTT EVENTS ----------

def mqtt_stat_Steckdose2_POWER_event(data):
    global led4, msg
    msg = (data[1]).decode()
    led4.on() if msg == 'ON' else led4.off()
    print("Steckdose2:", msg)


def mqtt_stat_Steckdose1_POWER_event(data):
    global led3, msg
    msg = (data[1]).decode()
    led3.on() if msg == 'ON' else led3.off()
    print("Steckdose1:", msg)


# ---------- MQTT CONNECT / RECONNECT ----------

def mqtt_connect():
    global mqtt_client
    print("MQTT connecting...")

    try:
        mqtt_client = MQTTClient('CoreS3', '192.168.0.100', port=1883,
                                 user='', password='', keepalive=60)

        mqtt_client.connect(clean_session=False)

        mqtt_client.subscribe('stat/Steckdose2/POWER', mqtt_stat_Steckdose2_POWER_event, qos=0)
        mqtt_client.subscribe('stat/Steckdose1/POWER', mqtt_stat_Steckdose1_POWER_event, qos=0)

        print("MQTT connected & subscribed.")
        time.sleep(0.2)
    except Exception as e:
        print("MQTT connect failed:", e)
        time.sleep(2)


# ---------- BUTTON EVENTS ----------

def button4_pressed_event(event_struct):
    page0.screen_load()

def button0_pressed_event(event_struct):
    page1Licht.screen_load()

def button3_released_event(event_struct):
    mqtt_client.publish('cmnd/Steckdose2/POWER', 'TOGGLE', qos=0)

def button2_released_event(event_struct):
    mqtt_client.publish('cmnd/Steckdose1/POWER', 'TOGGLE', qos=0)


# ---------- UI EVENT HANDLER ----------

def button4_event_handler(event_struct):
    if event_struct.code == lv.EVENT.PRESSED:
        button4_pressed_event(event_struct)

def button0_event_handler(event_struct):
    if event_struct.code == lv.EVENT.PRESSED:
        button0_pressed_event(event_struct)

def button3_event_handler(event_struct):
    if event_struct.code == lv.EVENT.RELEASED:
        button3_released_event(event_struct)

def button2_event_handler(event_struct):
    if event_struct.code == lv.EVENT.RELEASED:
        button2_released_event(event_struct)


# ---------- SETUP ----------

def setup():
    global page0, page1Licht, button0, button1, Akkubar2, led0, led2, charge, button2, button3, led3, led4, button4

    M5.begin()
    Widgets.setRotation(1)
    m5ui.init()

    page0 = m5ui.M5Page(bg_c=0x000000)
    page1Licht = m5ui.M5Page(bg_c=0x000000)
    button0 = m5ui.M5Button(text="Licht", x=114, y=23, bg_c=0x2196f3, text_c=0xffffff, font=lv.font_montserrat_24, parent=page0)
    button1 = m5ui.M5Button(text="Automation", x=71, y=137, bg_c=0x2196f3, text_c=0xffffff, font=lv.font_montserrat_24, parent=page0)
    Akkubar2 = m5ui.M5Bar(x=4, y=220, w=100, h=13, min_value=0, max_value=100, value=25, bg_c=0x2193f3, color=0x21f326, parent=page1Licht)
    led0 = m5ui.M5LED(x=7, y=187, size=20, color=0x00ff00, on=True, parent=page1Licht)
    led2 = m5ui.M5LED(x=297, y=215, size=20, color=0x00ff00, on=True, parent=page0)
    charge = m5ui.M5Label("CHAR", x=248, y=217, text_c=0xffffff, bg_c=0xffffff, bg_opa=0, font=lv.font_montserrat_14, parent=page0)
    button2 = m5ui.M5Button(text="Steckdose 1 (PC)", x=12, y=9, bg_c=0x2196f3, text_c=0xffffff, font=lv.font_montserrat_24, parent=page1Licht)
    button3 = m5ui.M5Button(text="Steckdose 2", x=14, y=78, bg_c=0x2196f3, text_c=0xffffff, font=lv.font_montserrat_24, parent=page1Licht)
    led3 = m5ui.M5LED(x=263, y=10, size=44, color=0x00ff00, on=True, parent=page1Licht)
    led4 = m5ui.M5LED(x=263, y=78, size=44, color=0x00ff00, on=True, parent=page1Licht)
    button4 = m5ui.M5Button(text="Back", x=227, y=196, bg_c=0x2196f3, text_c=0xffffff, font=lv.font_montserrat_24, parent=page1Licht)

    button4.add_event_cb(button4_event_handler, lv.EVENT.ALL, None)
    button0.add_event_cb(button0_event_handler, lv.EVENT.ALL, None)
    button3.add_event_cb(button3_event_handler, lv.EVENT.ALL, None)
    button2.add_event_cb(button2_event_handler, lv.EVENT.ALL, None)

    page0.screen_load()
    mqtt_connect()

    Power.setChargeCurrent(1000)
    Power.setChargeVoltage(4100)


# ---------- LOOP ----------

def loop():
    global last_ui_update

    # ---- MQTT schnell abfragen -> verhindert Verzögerungen
    for _ in range(5):
        try:
            mqtt_client.check_msg()
        except:
            mqtt_connect()

    if not mqtt_client.isconnected():
        mqtt_connect()

    # ---- UI nur alle 100ms aktualisieren (entkoppelt)
    now = time.ticks_ms()
    if time.ticks_diff(now, last_ui_update) > 100:
        last_ui_update = now

        M5.update()
        Akkubar2.set_value(Power.getBatteryLevel(), True)
        led2.on() if Power.isCharging() else led2.off()
        led0.on() if mqtt_client.isconnected() else led0.off()


# ---------- MAIN ----------

if __name__ == '__main__':
    try:
        setup()
        while True:
            loop()
    except (Exception, KeyboardInterrupt) as e:
        try:
            m5ui.deinit()
            from utility import print_error_msg
            print_error_msg(e)
        except ImportError:
            print("please update to latest firmware")

That is working instant, and over a long time. the led indicator switches instant and real.
The issue is, that the LVGL render takes so long, that the subscribed message dont come trough. its a bug in the blockly implementation, but it never gets fixed, because it seems, the M5Stack is abadoned....so u have to fix it in the mircopython code - and never get back to blockly - or u loose the code ^^