Works for me; likely an environmental problem. Make sure the compiler is using the WiFiMulti.h inside the esp32 directory, not an Arduino version (preferences->show verbose output during compile). If you installed manually, make sure you have run get.exe.

which library is that. I have used Arduino_MultiWiFi. after deleting it, I've used WiFiMulti_Generic, but also no success.
Where can I find this library, which offers setAllowOpenAP. Can you supply github reference pls.

WiFiMulti is part of the arduino-esp32 base. You don't need to install any additional library, and actually need to uninstall any other WiFiMulti.h.

no success
I get this output:
Dependency Graph |-- M5Unified @ 0.2.5 |-- I2C BM8563 RTC @ 1.0.4 |-- M5GFX @ 0.2.6+sha.d7fea53 |-- Time @ 1.6.1 |-- SolarCalculator @ 2.0.1 |-- minIniFS @ 1.0.1 |-- ArduinoJson @ 7.4.1 |-- SD @ 2.0.0 |-- WiFi @ 2.0.0 |-- HTTPClient @ 2.0.0 Building in release mode

Error:
Compiling .pio/build/esp32-s3-devkitm-1/src/main.cpp.o In file included from src/main.cpp:44: src/EPDWifi.h: In function 'void WiFi_enable()': src/EPDWifi.h:121:11: error: 'class WiFiMulti' has no member named 'setAllowOpenAP' WiFimulti.setAllowOpenAP(WiFi_useOpenAP); ^~~~~~~~~~~~~~ In file included from src/main.cpp:52:

my platformio.ini within vcode:

[env:esp32-s3-devkitm-1] ;platform = espressif32 platform = platformio/espressif32 board = esp32-s3-devkitm-1 framework = arduino board_build.partitions = default_16MB.csv board_upload.flash_size = 16MB board_upload.maximum_size = 16777216 board_build.arduino.memory_type = qio_opi monitor_speed = 115200 build_flags = -DBOARD_HAS_PSRAM -DARDUINO_USB_CDC_ON_BOOT=1 -DARDUINO_USB_MODE=1 lib_deps = m5stack/M5Unified tanakamasayuki/I2C BM8563 RTC guerratron/minIniFS paulstoffregen/Time jpb10/SolarCalculator guerratron/minIniFS bblanchon/ArduinoJson M5GFX=https://github.com/m5stack/M5GFX.git#develop
include of my sketch:
#include <M5Unified.h> #undef USE_M5_FONT_CREATOR #include "Data.h" #include "WiFi.h" #include "WiFiMulti.h" #include "time.h" #include "Utils.h" #include "NMEA.h"

If I click on go to definition, I get the following info:
It's code for esp8266. Function setAllowOpenAP is not included. How to setup platformio, to get the right S3 library?

• @file WiFiMulti.cpp
• @Date 16.05.2015
• @author Markus Sattler
• Copyright (c) 2015 Markus Sattler. All rights reserved.
• This file is part of the esp8266 core for Arduino environment.

Remove anything from your lib directory that is included in the platform libraries- WiFi, WiFiMulti and HTTPClient. Your environment seems damaged, and I can't know what you did to get there. You may need to wipe out the .pio directory and start over. The WiFiMulti in esp32 still has the old info from esp8266 (@SuGlider )

I have removed platformlib and all in .pio. But it installs the old esp8266 version.

in my plattformio.ini:
platform = espressif32
board = esp32-s3-devkitm-1
framework = arduino

The chip on the board is: ESP32_S3R8