Making a copy/clone of a "List<List<Map>>" - flutter

Question

I'm trying to create a copy/clone of a "List<List<Map'>>".
So far I tried:
dataFTY2 = dataFTY.map((element)=>element).toList();
dataFTY2 = json.decode(json.encode(dataFTY));
dataFTY2 = List.from(dataFTY);
Nothing seems to work. Whenever I change the copy "dataFTY2", dataFTY changes as well. I need this to be a completely independent copy. Please help. I cant seem to figure this out, its driving me crazy.
More code added for reference.
List failureDetails = [];
List trackIDs = [];
List dateTime = [];
var dataFTY2 = dataFTY.map((element) => element.map((ele) => Map.from(ele)).toList()).toList();
// get historyData for each one and sort through "F"s and put them into the table in a row?
for (var x in dataFTY2[4]) {
trackIDs.add(x["track_id"]);
dateTime.add(x["datetime"]);
}
List failuresOnly = List.filled(trackIDs.length, {}, growable: true);
for (var i = 0; i < trackIDs.length; i++) {
await fetchTrackIDTestDetails(context, trackIDs[i], dateTime[i], false);
failureDetails.add(MyGlobals().getTestCodeDetailsData());
}
//filter out only "F"s
for (var p = 0; p < failureDetails.length; p++) {
for (var t in failureDetails[p][0]) {
if (t["Status"] == "F") {
//add it to list, if pass do nothing
failuresOnly[p] = t;
}
}
}
//combine with FTY failure data, don't use new screen use old screen and toggle when pressed, add column on right side
//dataFTY2 = MyGlobals().getFTYFailureMoreDetails();
for (var i = 0; i < dataFTY2[4].length; i++) {
dataFTY2[4][i]["TestCode"] = failuresOnly[i]["TestCode"];
dataFTY2[4][i]["Status"] = failuresOnly[i]["Status"];
dataFTY2[4][i]["TestValue"] = failuresOnly[i]["TestValue"];
dataFTY2[4][i]["Lo_Limit"] = failuresOnly[i]["Lo_Limit"];
dataFTY2[4][i]["Up_Limit"] = failuresOnly[i]["Up_Limit"];
dataFTY2[4][i]["ProcTime"] = failuresOnly[i]["ProcTime"];
}

Answer 1

You can use Map.from named constructor to clone the Map like this,
dataFTY2 = dataFTY.map((element) => element.map((ele) => Map.from(ele)).toList()).toList();

Answer 2

I find it more straightforward to use collection-for and the spread (...) operator:
void main() {
var original = [
[
{'foo': 1, 'bar': 2},
{'foo': 3, 'bar': 4},
]
];
// Create a new List...
var copy = [
for (var sublist in original)
// ... where each element is a new List...
[
for (var map in sublist)
// ... where each element of the sublist is a new Map that
// copies all entries from `map`.
{...map},
],
];
original[0][0]['foo'] = -1;
print(original); // Prints: [[{foo: -1, bar: 2}, {foo: 3, bar: 4}]]
print(copy); // Prints: [[{foo: 1, bar: 2}, {foo: 3, bar: 4}]]
}