ESP32 in Arduino-IDE with FS.h and SPIFFS

I'm working on a webserver on ESP32 in Arduino IDE and would like to load an html-file. Tried to use SPIFFS.open from the library FS.h from github. Errormessage says SPIFFS was not declared in this scope. (As far as I can see, there's no bracket in the wrong place.)

I did not find any example for ESP32 and FS.h and desperately hope for some help. Thanks in advance.

Here is my code:

    #include "FS.h"
    #include "WiFi.h"


/Wifi Access data/
const char* ssid_ap = "AccessPoint";
const char* password_ap = "12345678"; 

const char * ssid_sta     = "";
const char * password_sta = "";

/* set global variables */
byte WiFiMode = 0;  // WIFI_STA = 1 = Workstation  WIFI_AP = 2  = Accesspoint
int request_counter;
String sHTML;
String sHTMLRequest;

/* Create instance of server on Port 80 */
WiFiServer server(80);
WiFiClient client;

/*
 * ******SETUP*******************************************************
 */
void setup() {

/initialize GPIO/

/*start serial communication */
  Serial.begin(115200);
  SPIFFS.format();
  Serial.println("Spiffs formatted");

/* start WiFi as workstation (STA), if not possible 
   start as Acess Point
   initialize server */ 
  WiFi_Start_STA();
  if (WiFiMode == 0) WiFi_Start_AP();
}

/*
 * **LOOP*************************************************************
 */
void loop() {

/* Check if a client has connected */
  client = server.available();
  if (!client) 
  {
    return;
  }

/*Wait for the client to send data */
  Serial.println("neuer Client verbunden");
  /*Count Aufruf der Seite: */
  request_counter ++; 
  unsigned long clTimeout = millis()+250;
  while(!client.available() && (millis()clTimeout) 
  { 
    Serial.println("time-out bei Client-Verbindung!");
    return; 
  }

/****** open html files  *******/
 SPIFFS.begin();
 File f = SPIFFS.open("/home.txt", "r");
    if (!f) {
    Serial.println("file open failed");
    }
    f.close();

}

/**********************************************************************
 * 
 **************** FUNCTIONS ********************************************
 * 



*/

/*
 * Fct tries to start WiFi in workstation mode, 
 * if not possible sets WiFiMode=AP 
 * starts server
 */
void WiFi_Start_STA() {
  unsigned long timeout;

WiFi.mode(WIFI_STA);   //  Try to start WiFi as Workstation

WiFi.begin(ssid_sta, password_sta);
  timeout = millis() + 12000L;
  while (WiFi.status() != WL_CONNECTED && millis() < timeout) {
  delay(10);
  }

if (WiFi.status() == WL_CONNECTED) {
    server.begin();
    WiFiMode = WIFI_STA;

Serial.print("Verbunden mit IP - Addresse: ");
    for (int i = 0; i < 3; i++) {
      Serial.print( WiFi.localIP()[i]);
      Serial.print(".");
    }
    Serial.println(WiFi.localIP()[3]);

} 
  else {
    WiFi.mode(WIFI_OFF);

Serial.println("WLAN-Verbindungsaufbau fehlgeschlagen");
}


}

/*
 *starts WiFi in AP-mode
 *starts server
 */
void WiFi_Start_AP() {
  WiFi.mode(WIFI_AP);   // Access Point mode
  WiFi.softAP(ssid_ap, password_ap);
  server.begin();       // start server
  IPAddress ApIP = WiFi.softAPIP();   //read IP of Access Point
  WiFiMode = WIFI_AP;

Serial.print("ESP-Netzwerk: ");
  Serial.print(ssid_ap);
  Serial.print(" aufgebaut. ");
  Serial.print( " IP-Addresse: ");
  Serial.println(ApIP);
}

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