How to pass a integer data from arduino (serial UART) to an ESPHome?

ESPHome
5

It’s not so easy with esphome. For some reason unknown to me, esphome doesn’t have any sophisticated component for serial rx. You can use Uart component for tx and uart debug with dummy_receiver option like this:

uart:
  baud_rate: 115200
  debug:
    direction: BOTH
    dummy_receiver: false
    after:
      delimiter: "\n"
    sequence:
      - lambda: UARTDebug::log_string(direction, bytes);

Another option is external component. Have a look at this post:
Easy UART Parsing ESPHome Component - ESPHome - Home Assistant Community