You can simplify your function by using the copyTo function:

fun File.copyInputStreamToFile(inputStream: InputStream) {
    this.outputStream().use { fileOut ->
        inputStream.copyTo(fileOut)
    }
}

FileNotFoundException: testing-again.png: open failed: EROFS (Read-only file system)

You cannot save a file in the system folder so you must specify the path and save your image for example i saved the image in the DCIM folder below :

fun copyStreamToFile(inputStream: InputStream) {
    val storeDirectory = this.getExternalFilesDir(Environment.DIRECTORY_DCIM) // DCIM folder
    val outputFile = File(storeDirectory, "testing-again.png")
    inputStream.use { input ->
        val outputStream = FileOutputStream(outputFile)
        outputStream.use { output ->
            val buffer = ByteArray(4 * 1024) // buffer size
            while (true) {
                val byteCount = input.read(buffer)
                if (byteCount < 0) break
                output.write(buffer, 0, byteCount)
            }
            output.flush()
        }
    }
}

You will find your image in this path : /storage/emulated/0/Android/data/Your_Package_Name/files/DCIM

Here it is, input is your inputStream. Then use same File (name) and FileInputStream to read the data in future.

try {
    File file = new File(getCacheDir(), "cacheFileAppeal.srl");
    try (OutputStream output = new FileOutputStream(file)) {
        byte[] buffer = new byte[4 * 1024]; // or other buffer size
        int read;

        while ((read = input.read(buffer)) != -1) {
            output.write(buffer, 0, read);
        }
        
        output.flush();
    }
} finally {
    input.close();
}