Raising handlebars using a stem raiser on B'twin Triban 500
As mentioned in comments a steerer tube extender should not be user with a carbon fiber composite steerer tube. Less expensive CFC forks often have an aluminum steerer tube.

You may want to consider a stem with a greater angle that will give more handle bar rise before a steerer tube extender, that would be a stronger option.

Are you riding with hands on the drops of the bars, or on the higher brake hoods position? Most riders spend most of their time on the hoods. If you are riding on the  drops and that feels too low, try riding on the hoods.