> db.c.insert({});
> db.c.aggregate([{
    $project: {
        datePlus1Month: {
            $dateToString: {
                date: {
                    $dateAdd: {
                        startDate: {
                            $dateFromString:
                                {dateString: "2021-02-01T00:00:00.000", timezone: "UTC"}
                        },
                        unit: "month",
                        amount: 1,
                        timezone: "UTC"
                    }
                },
                timezone: "UTC"
            }
        }
    }
}])
{ "_id": ObjectId("603cbeb2ffe24760edc177bb"), "datePlus1Month": "2021-03-01T00:00:00.000Z" }
> db.c.aggregate([{
    $project: {
        datePlus1Month: {
            $dateToString: {
                date: {
                    $dateAdd: {
                        startDate: {
                            $dateFromString:
                                {dateString: "2021-02-01T00:00:00.000", timezone: "Europe/Sofia"}
                        },
                        unit: "month",
                        amount: 1,
                        timezone: "Europe/Sofia"
                    }
                },
                timezone: "Europe/Sofia"
            }
        }
    }
}])
{ "_id": ObjectId("603cbeb2ffe24760edc177bb"), "datePlus1Month": "2021-03-04T00:00:00.000Z" }
> db.c.aggregate([{
    $project: {
        datePlus1Month: {
            $dateToString: {
                date: {
                    $dateAdd: {
                        startDate: {
                            $dateFromString: {
                                dateString: "2021-02-01T00:00:00.000",
                                timezone: "America/New_York"
                            }
                        },
                        unit: "month",
                        amount: 1,
                        timezone: "America/New_York"
                    }
                },
                timezone: "America/New_York"
            }
        }
    }
}])
{ "_id": ObjectId("603cbeb2ffe24760edc177bb"), "datePlus1Month": "2021-03-01T00:00:00.000Z" }
> db.c.aggregate([{
    $project: {
        datePlus1Month: {
            $dateToString: {
                date: {
                    $dateAdd: {
                        startDate: {
                            $dateFromString:
                                {dateString: "2021-04-30T20:00:00.000", timezone: "UTC"}
                        },
                        unit: "month",
                        amount: 1,
                        timezone: "UTC"
                    }
                },
                timezone: "UTC"
            }
        }
    }
}])
{ "_id": ObjectId("603cbeb2ffe24760edc177bb"), "datePlus1Month": "2021-05-30T20:00:00.000Z" }
db.c.aggregate([{
    $project: {
        datePlus1Month: {
            $dateToString: {
                date: {
                    $dateAdd: {
                        startDate: {
                            $dateFromString: {
                                dateString: "2021-04-30T20:00:00.000",
                                timezone: "America/New_York"
                            }
                        },
                        unit: "month",
                        amount: 1,
                        timezone: "America/New_York"
                    }
                },
                timezone: "America/New_York"
            }
        }
    }
}])
{ "_id": ObjectId("603cbeb2ffe24760edc177bb"), "datePlus1Month": "2021-05-31T20:00:00.000Z" }