Hmmmm...I applied using the AN form. I didn't apply online. I'm guessing this is a new service coz there's no online application when I applied on November last year. I haven't encountered that question in the form. I supposed you should answer YES and see what the next question would be. I'm thinking it'll ask you about the details of your ILR and BRP card next.

Look at the guidance just in case.

https://www.gov.uk/government/public...itizen-form-an