Indexing for slow queries

I am having a lot of difficulty creating indexes that a query actually uses.

From the cloud console I find a slow query and try to index but the index is not used.
What index would be suggested for the query below

{
  "type": "command",
  "ns": "ONSITEDb.JobONSITE",
  "appName": "MongoDB Compass",
  "command": {
    "explain": {
      "find": "JobONSITE",
      "filter": {
        "type": "command",
        "ns": "ONSITEDb.JobONSITE",
        "command": {
          "aggregate": "JobONSITE",
          "pipeline": [
            {
              "$match": {
                "isComplete": false,
                "isShadow": false
              }
            },
            {
              "$sort": {
                "startTime": -1
              }
            },
            {
              "$skip": 0
            },
            {
              "$limit": 25
            }
          ],
          "allowDiskUse": true,
          "collation": {
            "locale": "en",
            "caseLevel": false,
            "caseFirst": "off",
            "strength": 1
          },
          "cursor": {},
          "$db": "ONSITEDb",
          "lsid": {
            "id": {
              "$uuid": "d9501227-e952-4804-90e5-5e9ecffae67d"
            }
          },
          "$clusterTime": {
            "clusterTime": {
              "$timestamp": {
                "t": 1639458374,
                "i": 4
              }
            },
            "signature": {
              "hash": {
                "$binary": "TDu/Mdszf8VHazHhf92PrXeSQWM=",
                "$type": "00"
              },
              "keyId": {
                "$numberLong": "7005581243098071042"
              }
            }
          }
        },
        "planSummary": "IXSCAN { isShadow: 1, isComplete: 1, startTime: -1 }",
        "keysExamined": 4524,
        "docsExamined": 25,
        "hasSortStage": true,
        "fromMultiPlanner": true,
        "cursorExhausted": true,
        "numYields": 214,
        "nreturned": 25,
        "queryHash": "B2211B92",
        "planCacheKey": "B572E649",
        "reslen": 9276866,
        "locks": {
          "Global": {
            "acquireCount": {
              "r": 215
            }
          },
          "Mutex": {
            "acquireCount": {
              "r": 1
            }
          }
        },
        "readConcern": {
          "level": "local",
          "provenance": "implicitDefault"
        },
        "writeConcern": {
          "w": "majority",
          "wtimeout": 0,
          "provenance": "implicitDefault"
        },
        "storage": {
          "data": {
            "bytesRead": 1361197792,
            "timeReadingMicros": 3505870
          },
          "timeWaitingMicros": {
            "cache": 1133
          }
        },
        "remote": "13.236.230.61:42954",
        "protocol": "op_msg",
        "durationMillis": 3880,
        "v": "5.0.5"
      },
      "skip": 0,
      "limit": 0,
      "maxTimeMS": 60000
    },
    "verbosity": "allPlansExecution",
    "lsid": {
      "id": {
        "$uuid": "1417e28f-1176-436e-9e1d-878c963765d7"
      }
    },
    "$clusterTime": {
      "clusterTime": {
        "$timestamp": {
          "t": 1639478103,
          "i": 1
        }
      },
      "signature": {
        "hash": {
          "$binary": "tepwiDQ0tMz8HoJ1a3ln5PPT6r8=",
          "$type": "00"
        },
        "keyId": {
          "$numberLong": "7005581243098071042"
        }
      }
    },
    "$db": "ONSITEDb"
  },
  "numYields": 70,
  "reslen": 7880,
  "locks": {
    "Global": {
      "acquireCount": {
        "r": 71
      }
    },
    "Mutex": {
      "acquireCount": {
        "r": 1
      }
    }
  },
  "readConcern": {
    "level": "local",
    "provenance": "implicitDefault"
  },
  "storage": {
    "data": {
      "bytesRead": 442375998,
      "timeReadingMicros": 1103006
    },
    "timeWaitingMicros": {
      "cache": 34
    }
  },
  "remote": "203.220.178.172:62443",
  "protocol": "op_msg",
  "durationMillis": 1136,
  "v": "5.0.5"
}