Uri getting null for Android 11 (R)

I want to create sub directory (custom folder) with text file and write string data in it. As in Android 11 there is restriction so i have done this code.

private val filepath = "mySubDirectory"
private val filename = "test.txt"

private fun writeExternalStorage(list: MutableList<String>) {
    if (VERSION.SDK_INT >= VERSION_CODES.Q) {
        val resolver = contentResolver
        val values = ContentValues()
        values.put(MediaStore.MediaColumns.DISPLAY_NAME, filename)
        values.put(MediaStore.MediaColumns.MIME_TYPE, "text/plain")
        values.put(
            MediaStore.MediaColumns.RELATIVE_PATH,
            Environment.DIRECTORY_DOCUMENTS + "/" + filepath
        )
        val uri = resolver.insert(MediaStore.Files.getContentUri("external"), values)
        Log.v("MYATGAGAA", uri!!.toString())
        val file = FileUtil.from(this, uri!!) as File
        Log.v("MYATGAGAA", file.absolutePath)
        try {
            file.parentFile.mkdirs()
            file.bufferedWriter().use { out ->
                for (item in list) {
                    Log.v("MYATGAGAA", item)
                    out.write(item)
                }
            }

        } catch (e: IOException) {
            Toast.makeText(this, "Error Q", Toast.LENGTH_LONG).show()
            return

        }
        Toast.makeText(this, "Saved for Q", Toast.LENGTH_LONG).show()


      }

But i m getting uri null at this line Log.v("MYATGAGAA", uri!!.toString())

I have already granted storage permission below:

 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
 <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
 <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE"></uses-permission>

For Android R devices i have manually checked

if (SDK_INT >= Build.VERSION_CODES.R) {
        try {
            val intent = Intent(Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION)
            intent.addCategory("android.intent.category.DEFAULT")
            intent.data =
                Uri.parse(String.format("package:%s", applicationContext.packageName))
            startActivityForResult(intent, 2296)
        } catch (e: Exception) {
            val intent = Intent()
            intent.action = Settings.ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION
            startActivityForResult(intent, 2296)
        }
    }

This is my FileUtil class.

class FileUtil {

companion object {

    private const val EOF = -1
    private const val DEFAULT_BUFFER_SIZE = 1024 * 4

    @Throws(IOException::class)
    fun from(context: Context, uri: Uri): File? {
        val inputStream: InputStream = context.contentResolver.openInputStream(uri)!!
        val fileName = getFileName(context, uri)
        val splitName = splitFileName(fileName)
        var tempFile: File = File.createTempFile(splitName[0], splitName[1])
        tempFile = rename(tempFile, fileName)
        tempFile.deleteOnExit()
        var out: FileOutputStream? = null
        try {
            out = FileOutputStream(tempFile)
        } catch (e: FileNotFoundException) {
            e.printStackTrace()
        }
        if (inputStream != null) {
            copy(inputStream, out!!)
            inputStream.close()
        }
        out?.close()
        return tempFile
    }

    private fun splitFileName(fileName: String): Array<String> {
        var name = fileName
        var extension = ""
        val i = fileName.lastIndexOf(".")
        if (i != -1) {
            name = fileName.substring(0, i)
            extension = fileName.substring(i)
        }
        return arrayOf(name, extension)
    }

    private fun getFileName(context: Context, uri: Uri): String {
        var result: String? = null
        if (uri.scheme.equals("content")) {
            val cursor: Cursor = context.contentResolver.query(uri, null, null, null, null)!!
            try {
                if (cursor != null && cursor.moveToFirst()) {
                    result =
                        cursor.getString(cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME))
                }
            } catch (e: Exception) {
                e.printStackTrace()
            } finally {
                if (cursor != null) {
                    cursor.close()
                }
            }
        }
        if (result == null) {
            result = uri.path
            val cut: Int = result!!.lastIndexOf(File.separator)
            if (cut != -1) {
                result = result.substring(cut + 1)
            }
        }
        return result
    }

    private fun rename(file: File, newName: String): File {
        val newFile = File(file.parent, newName)
        if (newFile != file) {
            if (newFile.exists() && newFile.delete()) {
                Log.d("FileUtil", "Delete old $newName file")
            }
            if (file.renameTo(newFile)) {
                Log.d("FileUtil", "Rename file to $newName")
            }
        }
        return newFile
    }

    @Throws(IOException::class)
    private fun copy(input: InputStream, output: OutputStream): Long {
        var count: Long = 0
        var n: Int
        val buffer = ByteArray(DEFAULT_BUFFER_SIZE)
        while (EOF != input.read(buffer).also { n = it }) {
            output.write(buffer, 0, n)
            count += n.toLong()
        }
        return count
    }
}
}

still getting error. So please help me to sort out this. Thanks in Advance