convert a String of “uint8list” to a Unit8List

codeUnits gets you a List<int>
Uint8List.fromList(...) converts List<int> to Uint8List
String.fromCharCodes(...) converts List<int> or Uint8List to String

List<int> list="xxx".codeUnits;
Uint8List bytes = Uint8List.fromList(list);
String string = String.fromCharCodes(bytes);