To address a man formally, use his first name + Bey (e.g., Kaan Bey, Guy Bey, Mehmet Bey, etc.) To address a woman formally, use her first name + Hanım (Selcen Hanım, Tuğba Hanım, Evrim Hanım, etc.)
Turkish does, however, have a formula similar to English where you use the last name, but it's reserved for very formal usage and I have not seen it much outside of addressing an envelope or in Turkish parliament: Sayın (esteemed)(gender neutral). Sayın Tekinoğlu, Sayın Gencebey, Sayın Kurt, etc. But again, it's not used as much as bey and hanım
I think this is a bit more common, although not as common as Murat Bey / Ayşe Hanım. One of my favourite bars in Istanbul is called "Baykuş" (no need to translate this to Duolingo folks), and, while the men's toilet has "Baykuş" written on the door, the women's has "Bayankuş"
The trouble is the UK translation is wrong as you would never say Mr Kaan as Mr is only used with a surname. I have to answer ın wrong English to get the answer marked correct. Just thinking a bit confusing for non English speakers. Just a thought maybe needs something added to explain it in the notes.