Arduino writes bluetooth input to the keyboard

bluetooth-keyboard.ino

#include <SoftwareSerial.h>
#include <Keyboard.h>

#define BLUETOOTH_RX 14  // Change this (RX)
#define BLUETOOTH_TX 16  // Change this (TX)

SoftwareSerial BTserial(BLUETOOTH_RX, BLUETOOTH_TX);

void setup() {
  Serial.begin(9600);
  BTserial.begin(9600);
  Serial.println("Serial and Bluetooth Serial ready");
  Keyboard.begin();
  Serial.println("Keyboard ready");
}

void loop() {
  if (BTserial.available()) {
    String s = "";
    char c;
    while((c = BTserial.read()) != -1) {
      s += c;
      delay(10);
    }
    
    int N = s.length() + 1;
    for (int i = 0; i < N; i++) {
      Keyboard.write(s[i]);
      delay(10);
    }
    Keyboard.write(0x0A);

    Serial.println("Bluetooth -> Arduino: " + s);
  }

  if (Serial.available()) {
    String s = "";
    char c;
    while((c = Serial.read()) != -1) {
      s += c;
      delay(10);
    }

    delay(10);

    Serial.println("Arduino -> Bluetooth: " + s);

    BTserial.print(s);
  }
}