Warning: This library is not ready yet. Atm keys can only be sent using the sendReport method. The code hasn't been tested at all. It should compile wihtout errors though.

Installation

(Make sure you can use the ESP32 with the Arduino IDE. Instructions can be found here.)
Download the latest release of this library from the release page.
In the Arduino IDE go to "Sketch" -> "Include Library" -> "Add .ZIP Library..." and select the file you just downloaded.
You can now go to "File" -> "Examples" -> "ESP32 BLE Keyboard" and select any of the examples to get started.

Example

/**
 * This example turns the ESP32 into a Bluetooth LE keyboard that types the letter `a` once every 5 seconds.
 */
#include <BleKeyboard.h>

BleKeyboard bleKeyboard;

void setup() {
  Serial.begin(115200);
  Serial.println("Starting BLE work!");
  bleKeyboard.begin();
}

void loop() {
  if(bleKeyboard.isConnected()) {
    Serial.println("Pressing the a-key via the Bluetooth keyboard");

    KeyReport keyReport;
    keyReport.modifiers = 0x00;
    keyReport.reserved = 0x00;
    keyReport.keys[0] = 0x61; // a-key
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;

    bleKeyboard.sendReport(&keyReport); // a-key down

    delay(50);

    KeyReport keyReport2;
    keyReport.modifiers = 0x00;
    keyReport.reserved = 0x00;
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;
    keyReport.keys[0] = 0x00;

    bleKeyboard.sendReport(&keyReport2); // a-key up

  }
  delay(5000);
}

API docs

The BleKeyboard interface is almost identical to the Keyboard Interface, so you can use documentation right here: https://www.arduino.cc/reference/en/language/functions/usb/keyboard/

Just remember that you have to use bleKeyboard instead of just Keyboard and you need these two lines at the top of your script:

#include <BleKeyboard.h>
BleKeyboard bleKeyboard;

There is also Bluetooth specific information that you can set (optional): Instead of BleKeyboard bleKeyboard; you can do BleKeyboard bleKeyboard("Bluetooth Device Name", "Bluetooth Device Manufacturer", 100);. The third parameter is the initial battery level of your device. To adjust the battery level later on you can simply call e.g. bleKeyboard.setBatteryLevel(50) (set battery level to 50%). By default the battery level will be set to 100%, the device name will be ESP32 Bluetooth Mouse and the manufacturer will be Espressif.

Credits

Credits to chegewara as this library is based on this piece of code that he provided.