var options = new JsonSerializerOptions()
{
    Converters =
    {
        new Cysharp.Serialization.Json.UlidJsonConverter()
    }
};

JsonSerializer.Serialize(Ulid.NewUlid(), options);

var resolver = MessagePack.Resolvers.CompositeResolver.Create(
    Cysharp.Serialization.MessagePack.UlidMessagePackResolver.Instance,
    MessagePack.Resolvers.StandardResolver.Instance);
var options = MessagePackSerializerOptions.Standard.WithResolver(resolver);

MessagePackSerializer.Serialize(Ulid.NewUlid(), options);

public class BinaryUlidHandler : TypeHandler<Ulid>
{
    public override Ulid Parse(object value)
    {
        return new Ulid((byte[])value);
    }

    public override void SetValue(IDbDataParameter parameter, Ulid value)
    {
        parameter.DbType = DbType.Binary;
        parameter.Size = 16;
        parameter.Value = value.ToByteArray();
    }
}

public class StringUlidHandler : TypeHandler<Ulid>
{
    public override Ulid Parse(object value)
    {
        return Ulid.Parse((string)value);
    }

    public override void SetValue(IDbDataParameter parameter, Ulid value)
    {
        parameter.DbType = DbType.StringFixedLength;
        parameter.Size = 26;
        parameter.Value = value.ToString();
    }
}

// setup handler
Dapper.SqlMapper.AddTypeHandler(new BinaryUlidHandler());

public class UlidToBytesConverter : ValueConverter<Ulid, byte[]>
{
    private static readonly ConverterMappingHints defaultHints = new ConverterMappingHints(size: 16);

    public UlidToBytesConverter(ConverterMappingHints mappingHints = null)
        : base(
                convertToProviderExpression: x => x.ToByteArray(),
                convertFromProviderExpression: x => new Ulid(x),
                mappingHints: defaultHints.With(mappingHints))
    {
    }
}

public class UlidToStringConverter : ValueConverter<Ulid, string>
{
    private static readonly ConverterMappingHints defaultHints = new ConverterMappingHints(size: 26);

    public UlidToStringConverter(ConverterMappingHints mappingHints = null)
        : base(
                convertToProviderExpression: x => x.ToString(),
                convertFromProviderExpression: x => Ulid.Parse(x),
                mappingHints: defaultHints.With(mappingHints))
    {
    }
}