[<JsonFSharpConverter(BaseUnionEncoding = _)>] not being honored

Example:

[<JsonFSharpConverter(BaseUnionEncoding = JsonUnionEncoding.Untagged)>]
type Sql =
  | Sql of sql: string
  | SqlId of sqlId: int
  
let options =
  JsonFSharpOptions.Default()
    .WithAllowOverride(true)
    .ToJsonSerializerOptions()

JsonSerializer.Serialize(Sql "select *", options)

type Sql =
  | Sql of sql: string
  | SqlId of sqlId: int
val options: JsonSerializerOptions
val it: string = "{"Case":"Sql","Fields":["select *"]}"

Expecting {"sql":"select *"} .

Start with the F# reproduction using JsonFSharpConverter, JsonFSharpOptions.Default(), and JsonUnionEncoding.Untagged, then compare the actual serialization with the expected output. Trace why the attribute is not honored when JsonSerializer.Serialize is called; done means the example produces {"sql":"select *"}.