(including my modifications) diff.yaml

mqtt:
  broker: "< ip >"
  port: 1883
  username: "<username>"
  password: "<password>"
  discovery: true
  topic_prefix: "megadesk"

  on_message:
    - topic: "megadesk/set/height"
      then:
        - lambda: |-
            int raw_value = atoi(x.c_str());  // Convert MQTT message to integer
            if (raw_value >= 299 && raw_value <= 6640) {
              ESP_LOGI("MQTT", "Setting desk height (raw) to: %d", raw_value);
  
              // Update the UI state
              id(megadesk_height_raw).publish_state(raw_value);
  
              // Use the same set_action code as the slider
              char buf[20];
              sprintf(buf, "<=%d.", raw_value);
              id(uart_desk).write_str(buf);
              ESP_LOGI("MQTT", "Sent UART command: %s", buf);
            } else {
              ESP_LOGW("MQTT", "Invalid raw height value: %d", raw_value);
            }

(original file) megadesk-companion.yaml

# If you get errors compiling this with esphome, make sure you are on a recent version.
# 'esphome version' will output the version you are on.
#
# If you want to compile in the Home Assistant esphome addon, you need to copy megadesk.h into your esphome folder
# on your Home Assistant platform.

esp32:
  board: esp32-c3-devkitm-1
  framework:
    type: esp-idf
    version: recommended

esphome:
  name: megadesk
  comment: megadesk-companion
  platformio_options:
    board_build.flash_mode: dio # If you don't specify this using esp-idf framework, the device will boot-loop.
  includes:
    - megadesk.h
  on_boot:
    priority: -100
    then:
      - delay: 1s
      - uart.write: "<C0.0."
      - delay: 1s
      - uart.write: "<R0.11."
      - delay: 1s
      - uart.write: "<R0.12."

#####
# You need to make sure tx_pin and rx_pin are set properly for your device.
# For 5-pin Megadesks, this will not need changing.
#
# If you have a 3-pin megadesk, try swapping them in case of a mixup on RX/TX
# when you soldered the wires.
#####
uart:
  id: uart_desk
  baud_rate: 115200
  tx_pin: GPIO6
  rx_pin: GPIO7

logger:
  hardware_uart: USB_SERIAL_JTAG # Logging over the USB-C port (WiFi will always log as well)

api:
  password: ""

ota:
  - platform: esphome
    password: ""

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

  ap:
    ssid: "Companion Fallback"
    password: "megadesk"

captive_portal:

web_server:
  port: 80

sensor:
  - platform: custom
    lambda: |-
      auto megadesk = new Megadesk(id(uart_desk));
      App.register_component(megadesk);
      return { megadesk->raw_height, megadesk->min_height, megadesk->max_height };
    sensors:
    - id: megadesk_raw
      internal: true
      on_value:
        then:
          - component.update: megadesk_height_inches
          - component.update: megadesk_height_cm
          - component.update: megadesk_height_raw
    - name: "Megadesk Minimum Height"
    - name: "Megadesk Maximum Height"

number:
  - platform: template
    name: "Megadesk Height (inches)"
    id: megadesk_height_inches
    min_value: 23
    max_value: 47
    step: 0.53
    mode: slider
    update_interval: never
    unit_of_measurement: 'inches'
    #NewValue = (((OldValue - OldMin) * (NewMax - NewMin)) / (OldMax - OldMin)) + NewMin
    lambda: |-
      return ((((id(megadesk_raw).state - 299) * (47 - 23)) / (6914 - 299)) + 23);
    set_action:
      - number.set:
          id: megadesk_height_raw
          value: !lambda "return int((((x - 23) * (6914 - 299)) / (47 - 23)) + 299);"
  - platform: template
    name: "Megadesk Height (cm)"
    id: megadesk_height_cm
    min_value: 58.42
    max_value: 118.745
    step: 0.53
    mode: slider
    update_interval: never
    unit_of_measurement: 'cm'
    #NewValue = (((OldValue - OldMin) * (NewMax - NewMin)) / (OldMax - OldMin)) + NewMin
    lambda: |-
      return ((((id(megadesk_raw).state - 299) * (119.38 - 58.42)) / (6914 - 299)) + 58.42);
    set_action:
      - number.set:
          id: megadesk_height_raw
          value: !lambda "return int((((x - 58.42) * (6640 - 299)) / (119.38 - 58.42)) + 299);"
  - platform: template
    name: "Megadesk Height (raw)"
    id: megadesk_height_raw
#    internal: true
    min_value: 299
    max_value: 6640
    step: 1
    mode: slider
    update_interval: never
    lambda: |-
      return id(megadesk_raw).state;
    set_action:
      - uart.write: !lambda |-
          char buf[20];
          sprintf(buf, "<=%i,.", int(x));
          std::string s = buf;
          return std::vector<unsigned char>( s.begin(), s.end() );

button:
  - platform: template
    name: "Desk Position 2"
    on_press:
      then:
        - uart.write: "<L0,2."
  - platform: template
    name: "Desk Position 3"
    on_press:
      then:
        - uart.write: "<L0,3."
  - platform: template
    name: "Desk Position 4"
    on_press:
      then:
        - uart.write: "<L0,4."
  - platform: template
    name: "Desk Position 5"
    on_press:
      then:
        - uart.write: "<L0,5."
  - platform: template
    name: "Toggle Minimum Desk Height"
    on_press:
      then:
        - uart.write: "<L0,11."
        - uart.write: "<R0,11."
  - platform: template
    name: "Toggle Maximum Desk Height"
    on_press:
      then:
        - uart.write: "<L0,12."
        - uart.write: "<R0,12."
  - platform: template
    name: "Recalibrate Desk"
    on_press:
      then:
        - uart.write: "<L0,14."
  - platform: template
    name: "Reboot Megadesk"
    on_press:
      then:
        - uart.write: "<L0,15."
  - platform: template
    name: "Toggle Audio feedback"
    on_press:
      then:
        - uart.write: "<L0,17."
  - platform: template
    name: "Toggle both-button mode"
    on_press:
      then:
        - uart.write: "<L0,18."

interval:
  - interval: 300s
    then:
      - uart.write: "<C0.0."