System.Text.Json converter for Either<UnsupportedValue, T> - useful where T is an enum from a 3rd party API and you want to handle unknown values

EitherValidOrUnsupportedValueConverter.cs

internal class EitherValidOrUnsupportedValueConverterFactory : JsonConverterFactory
{
    public override bool CanConvert(Type typeToConvert)
    {
        var canConvert = typeToConvert.IsGenericType && typeToConvert.GetGenericTypeDefinition() == typeof(Either<,>) && typeToConvert.GenericTypeArguments[0] == typeof(UnsupportedValue);
        return canConvert;
    }

    public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options)
    {
        typeToConvert = typeToConvert.GenericTypeArguments[1];
        return (JsonConverter)Activator.CreateInstance(typeof(EitherValidOrUnsupportedValueConverter<>).MakeGenericType(typeToConvert));
    }
}

internal class EitherValidOrUnsupportedValueConverter<T> : JsonConverter<Either<UnsupportedValue, T>>
{
    public override Either<UnsupportedValue, T> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        try
        {
            var deserialized = JsonSerializer.Deserialize<T>(ref reader, options);
            return deserialized;
        }
        catch (JsonException ex)
        {
            return UnsupportedValue.Instance;
        }
    }

    public override void Write(Utf8JsonWriter writer, Either<UnsupportedValue, T> value, JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }
}    
    
public record UnsupportedValue
{
    public static readonly UnsupportedValue Instance = new UnsupportedValue();

    private UnsupportedValue()
    {
    }
}

For anyone that uses System.Text.Json to consume a 3rd party API (esp where the API returns enum type values) you might find this converter handy.

Let's say nominally your DTO looks like this:

public class GoogleApiResponseDto
{
    public DayOfWeek Day { get; set; }

    public string SomeOtherField { get; set; }
}

But what if Google invents a new day like DeepFriday but doesn't tell you about it (or they tell you but you are too busy/forget)?
Well you can define your DTO like this instead for deserializing

public class GoogleApiResponseDto
{
    public Either<UnsupportedValue, DayOfWeek> Day { get; set; }

    public string SomeOtherField { get; set; }
}

You can still get the rest of the information from the DTO, and possibly gracefully handle the unsupported case somehow.
Note - this would mean modifying your code obviously (because now you need to handle both the cases where Day is a supported DayOfWeek value as well as cases where it's an UnsupportedValue.