Am more convinced to mention the name at birth because the column on the far right Have a section and among of selections is “Name at Birth”.I dont think thats quite right. It clearly says in the instruction guide -
https://www.canada.ca/en/immigration-refugees-citizenship/services/application/application-forms-guides/guide-0002-application-canadian-citizenship-under-subsection-5-1-adults-18-years-older.html#Step4
We need to know all of the names you have ever used in order to verify your identity. If you used any other names other than the one being requested in your grant of citizenship application, print them in the chart. Examples: Name at time of birth, name before marriage, previous married names, married name, nick names or any other names you have used. If you have legally changed your name, see Appendix A – Changing the name on your document.
To be on the safe side - we put it as N/A.
So, if you never change your name you can just write your name and choose “Name of birth”