Maybe a stacked widget like this?

Row(
  mainAxisAlignment: MainAxisAlignment.center,
  crossAxisAlignment: CrossAxisAlignment.end,
  children: [
    Text('this '),
    CaretLetter('7'),
    Text(' is custom'),
  ],
),

class CaretLetter extends StatelessWidget {
  final String s;
  const CaretLetter(this.s, {super.key});

  @override
  Widget build(BuildContext context) {
    return Stack(
      alignment: AlignmentDirectional.topCenter,
      children: [
        Text('\u0302'),
        Padding(padding: const EdgeInsets.fromLTRB(0, 4, 0, 0), child: Text(s)),
      ],
    );
  }
}