You should add the value attribute to each of your input fields:
<input type="radio" name="options" id="option1" value="option1"> Option1 </input><br>
<input type="radio" name="options" id="option2" value="option2"> Option2 </input><br>
<input type="radio" name="options" id="option3" value="option3"> Option3 </input><br>
and in your flask route you can read the selected option:
option = request.form['options']
and you’ll get the value of the selected radio button.