Mongodb findoneandupdate with aggregation pipeline

Try using $map to change the $sum's input structure:

PM.findOneAndUpdate(    {        _id: MongoId,    },    [        {            $set: {                TotalAmt: {                    $cond: {                        if: {$gte: ['$dtl.amt', 10]},                        then: {                            $sum: {                                $map: {                                   input: '$dtl',                                   as: "item",                                   in: "$$item.amt"                                 }                            },                        },                             else: 0, // 0 or "$TotalAmt" ?                     },                },            },        },    ],    {new: true})

You need to use $filter operator:

PM.findOneAndUpdate(  {    _id: MongoId,  },  [    {      $set: {        TotalAmt: {           $sum: {            $filter: {              input: '$dtl.amt',              cond: { $gte: ['$$this', 10] }            }          }        }      }    }  ]  { new: true })

---Output---

{    "_id" : ObjectId("5ec4ed0b94996124187b95ce"),    "cid" : "245345323",    "dtl" : [         {            "_id" : ObjectId("5ed5ab655df7930ec424be1e"),            "sid" : "test",            "amt" : 48,            "Name" : "test"        },         {            "_id" : ObjectId("5ed5ac9f79a75423d4bc0270"),            "sid" : "s",            "amt" : 14,            "Name" : "sfds"        },         {            "_id" : ObjectId("5ed5ace7d204ab144863ed7a"),            "sid" : "wesad",            "amt" : 6,            "Name" : "2sdad"        }    ],    "updated" : ISODate("2020-05-20T08:40:43.787Z"),    "__v" : 6,    "TotalAmt" : 62}

Edit: If you want filter by other field, we need to add extra $map operator.

PM.findOneAndUpdate(  {    _id: MongoId,  },  [    {      $set: {        TotalAmt: {           $sum: {            $map:{                input: {                  $filter: {                    input: '$dtl',                    cond: { $eq: ['$$this.Name', 'test'] }                  }                },                in:"$$this.amt"            }          }        }      }    }  ],  { new: true })