For mongo version 4.2+ you can just use pipelined updates combined with $setUnion, like so:

db.collection.updateMany({},
[
  {
    $set: {
      Tags: {
        $setUnion: "$Tags"
      }
    }
  }
])

Mongo Playground

You can create a unique index on the tag property of the collection in question.

Please refer to the following official guide;

https://docs.mongodb.com/manual/core/index-unique/

This looks like a nice option to clean duplicates from mongo shell:

 db.collection.aggregate([
    { "$project": {
        "Tags": { "$setUnion": [ "$Tags", [] ] },
        "same": { "$eq": [
        { "$size": "$Tags" },
        { "$size": { "$setUnion": [ "$Tags", [] ] } }
    ]}
  }},
   { "$match": { "same": false } }
 ]).forEach(function(doc) {
 db.collection.update(
    { "_id": doc._id },
    { "$set": { "Tags": doc.Tags } }
  )
 })

explained:

1. project a new field "Tags" with only the unique values.
2. Project a new field "same" that will check and say if there is duplicates.
3. Match only the documents having duplicates
4. Loop with forEach over the documents having duplicate tags to replace with the unique version.