Error Invalid $set :: caused by :: ' emoji' starts with an invalid character for a user variable name

Working with Data
,
2

I have had the same problem recently after searching for possible solutions. I have come to this

db.test.bulkWrite([
   {
       "updateOne": {
           "filter": {"unique_id": "b4f5393a3a7f822eabd3d6eead66e533"},
           "update": [
               { "$set": { "remark": { $literal: "$$ emoji" }} }
           ],
           "upsert": true
       }
   }
]);

I have carried out satisfactory tests for the case “$$ emoji” and “$ emoji”