Create a Variable of Query type from MongoDB source

I would like to define a Variable of Query type from the MongoDB data source.
For this reason, I created a sample database trial_db and a table trial_table, with the following items:

[{
  "name": "A",
  "value": 5.3
},{
  "name": "A",
  "value": 5.8
},{
  "name": "A",
  "value": 6.2
},{
  "name": "B",
  "value": 6.8
},{
  "name": "B",
  "value": 1.2
}]

I would like to create a Grafana Variable from the distinct name fields (A and B in this case).
So, in the Query field of this variable, I selected the MongoDB data source, and inserted trial_db.trial_table.distinct("name") as query. It is not working: the “Preview of values” is None. And in the dashboard, the new variable appears, but I can only select None. So, this variable is not working, and I suspect that I am somehow misusing the MongoDB data source for this use case.

The MongoDB plugin works very well as a data source for panels, but it is not working for the definition of Variables.

What should I do? Is the MongoDB plugin supposed to work for the definition of Variables?

I am using Grafana 9.1.5.

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