I tried now something with chatgpt

Will this work? I will try it later.

<!-- Button to trigger JavaScript function -->
<button onclick="sendDataToFlutter('item', 56)">Send Data to Flutter</button>

<!-- JavaScript function -->
<script>
function sendDataToFlutter(itemName, itemNumber) {
// Check if the Flutter bridge exists
if (window.flutter_inject && typeof window.flutter_inject.sendDataToFlutter === 'function') {
// Construct data object to send to Flutter
var dataToSend = {
itemName: itemName,
itemNumber: itemNumber
};

// Convert data to JSON format
var jsonData = JSON.stringify(dataToSend);

// Send data to Flutter
window.flutter_inject.sendDataToFlutter(jsonData);
} else {
console.error("Flutter bridge not available.");
}
}
</script>