After upgrading to Version 1.4.34 I can no longer serialize simple enums, it works with the previous version 1.3.13
This code:
type Enum =
| Case1
| Case2
type Record =
{ Field: Enum }
let options =
JsonFSharpOptions
.Default()
.WithUnionUnwrapFieldlessTags()
.ToJsonSerializerOptions()
let json = JsonSerializer.Serialize({ Field = Enum.Case2 }, options)
Creates the following json