"İstanbul changed a lot."
Translation:İstanbul çok değişti.
No, it would mean: Istanbul has changed it a lot.
You're just not saying the "it". But the verb is now transitive, so we understand that Istanbul has changed something.
Ideally, I'd get it if you provided the said text in Turkish i.e. what is the Turkish for "Istanbul has been changed a lot". (i.e. passive)
The passive suffix is -il. But you need the verb in transitive form, so you also add the -dir: İstanbul çok değiştirildi.
Thinking further, might this be the correct version? İstanbul'u çok değiştirildi/miş.
no that makes no sense. in "istanbul çok değiştirildi" istanbul is the subject
No, that would be exactly like saying: "It was changed Istanbul a lot." i.e.; ungrammatical. "değiştirilmek" is in the passive voice, which means Istanbul is tge subject now: (Istanbul was changed). You can't add the accusative suffix anymore. It can't both be the subject and the object at the same time. Passive verbs can't have objects.