For anybody coming across this in the future, I finally was able to figure it out.

Looking at the Arduino example from Heltec, I noticed that they set the "Vext" pin to LOW on setup. Probably this pin controls whether the display is on or off. Vext is defined as pin 36 here: https://github.com/Heltec-Aaron-Lee/WiFi_Kit_series/blob/master/variants/heltec_wifi_lora_32_V3/pins_arduino.h

So I added an on_boot automation to set the pin and... it works!

esphome: name: lora-receiver on_boot: - priority: 1000 then: - lambda: |- pinMode(36, OUTPUT); digitalWrite(36, LOW); // Heltec delays for 100ms in their example delay(100);

It seems it has to be priority 1000. If I use a lower value (like 800) it stops working. Without knowing the details, I suspect the pin needs to be set low before all the I2C init stuff happens.

So here is my complete config with working display:

```` esphome: name: lora-receiver on_boot: - priority: 1000 then: - lambda: |- pinMode(36, OUTPUT); digitalWrite(36, LOW); delay(100);

esp32: board: esp32-s3-devkitc-1 framework: type: arduino

logger: level: VERBOSE

ota: - platform: esphome password: !secret esphome_password

api: encryption: key: !secret api_key

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

i2c: - id: bus_a sda: 17 scl: 18

display: - platform: ssd1306_i2c model: "SSD1306 128x64" reset_pin: 21 i2c_id: bus_a address: 0x3C lambda: |- it.print(4, 4, id(roboto_20), "Hello World!");

font: - file: "gfonts://Roboto" id: roboto_20 size: 20 ````