I have the following Setup:

ESP32 WROOM 32 1x connected with Pin 21 as SDA and Pin 22 SCL to PCA9548A I2C Multiplexer, that is connected with SDA 0 and SCL 0 to scanner 1, SDA 1 and SCL 1 to scanner 2 and SDA 2 and SCL 2 to scanner 3.

The NFC scanners are PN532.

The Code for it is that I made is:

#include <Wire.h>
#include <Adafruit_PN532.h>

#define TCAADDR 0x70 // TCA9548A I2C Multiplexer
#define PN532_I2C_ADDRESS 0x24 // Standard PN532 Adresse


Adafruit_PN532 scanner1(&Wire);
Adafruit_PN532 scanner2(&Wire);
Adafruit_PN532 scanner3(&Wire);

// Multiplexer Kanalwahl
void tcaSelect(uint8_t channel) {
    if (channel > 7) return;
    Wire.beginTransmission(TCAADDR);
    Wire.write(1 << channel); // Den Kanal aktivieren
    Wire.endTransmission();
    delay(10);
}

void setup() {
    Serial.begin(115200);
    Wire.begin(21, 22);

    // Scanner initialisieren
    tcaSelect(0);
    if (!scanner1.begin()) {
        Serial.println("Fehler: Scanner 1 konnte nicht initialisiert werden!");
    } else {
        Serial.println("Scanner 1 erfolgreich initialisiert.");
    }

    tcaSelect(1);
    if (!scanner2.begin()) {
        Serial.println("Fehler: Scanner 2 konnte nicht initialisiert werden!");
    } else {
        Serial.println("Scanner 2 erfolgreich initialisiert.");
    }

    tcaSelect(2);
    if (!scanner3.begin()) {
        Serial.println("Fehler: Scanner 3 konnte nicht initialisiert werden!");
    } else {
        Serial.println("Scanner 3 erfolgreich initialisiert.");
    }

    Serial.println("Setup abgeschlossen");
}

void readScanner(Adafruit_PN532 &scanner, uint8_t channel) {
    tcaSelect(channel);

    uint8_t success;
    uint8_t uid[] = {0, 0, 0, 0, 0, 0, 0};
    uint8_t uidLength;

    success = scanner.readPassiveTargetID(PN532_MIFARE_ISO14443A, uid, &uidLength);

    if (success) {
        Serial.println("Karte gefunden!");
        Serial.print("UID Länge: "); Serial.print(uidLength, DEC); Serial.println(" bytes");
        Serial.print("UID Wert: ");
        for (uint8_t i = 0; i < uidLength; i++) {
            Serial.print(" 0x"); Serial.print(uid[i], HEX);
        }
        Serial.println("");
        delay(1000);
    }
}

void loop() {
    readScanner(scanner1, 0);
    readScanner(scanner2, 1);
    readScanner(scanner3, 2);
    delay(1000);
}

The error Code is:

invalid conversion from "TwoWire*" to "uint8_t" {aka "unsigned char"} [-fpermissive]

I tried letting the scanner initialising like the following:

(Wire) (&Wire) (TwoWire) (&TwoWire) (21, 22)

nothing worked.

As much as I know, the problem is, that I try to initialize the scanners alone, but they all use the same I2C Address Bus. What I want to try, is to set the Modules over the Multiplexer as separate I2C addresses, I just don't know why.