Can modifiedCount and upsertedCount both be 0?

There are a few scenarios where both modifiedCount and upsertedCount can be 0:

• When a filter within the update operation does not match:

db.collection.updateOne(
    {_id: 2},
    { $set: { items.$[elem]: 4 } },
    { arrayFilters: [{elem: 3}], upsert: true }
)

In this example, the filter {elem: 3} will not match any element in the items array. As a result, the document will be found (setting matchedCount to 1), but no modifications will be made (setting both modifiedCount and upsertedCount to 0).
• When using $setOnInsert:

db.collection.updateOne(
  { name: "David" },
  { $setOnInsert: { firstSeenAt: new Date() } },
  { upsert: true }
)

In this example, if the document with name: "David" already exists, the update operation will not modify the document (setting modifiedCount to 0). However, since upsert is set to true, the firstSeenAt field will be set if the document does not exist, resulting in upsertedCount being 0 as well.