You can achieve this result with two different ways:
First, using hintText and suffixIcon, and then styling the hint:
TextField(
decoration: InputDecoration(
hintText: 'Hint Text',
hintStyle: TextStyle(color: Colors.red),
suffixIcon: Padding( //suffixIcon, this way it don't disapear when the TextField is unfocused
padding: EdgeInsets.only(top: 20), //padding to put closer to the line
child: Text(
'Right text',
style: TextStyle(
color: Colors.grey,
),
),
),
),
),
result:

Second way, using prefixIcon and suffixIcon:
TextField(
decoration: InputDecoration(
prefixIcon: Container(
margin: EdgeInsets.only(bottom: 10),
width: 50,
height: 10,
alignment: Alignment.center,
decoration: BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.circular(10),
),
child: Text('Text', style: TextStyle(color: Colors.white),),
),
suffixIcon: Padding(
padding: EdgeInsets.only(top: 20),
child: Text(
'Right text',
style: TextStyle(
color: Colors.grey,
),
),
),
),
),
result:
