Learn Farsi: آیا او کسی را مسدود کرده است؟

A compound verb has a non-verbal part (مسدود) and a verbal part (کردن). To make it present perfect, you leave the non-verbal part alone, turn the verb into its past participle (کرده), and add the present tense of 'to be' (است for 'he/she'). So, it becomes مسدود کرده است.

I learned that را is used for specific direct objects. Why is it used with کسی (anyone) here?

While را usually marks specific objects, indefinite pronouns like کسی (someone/anyone) and چیزی (something/anything) still take را when they are the direct object of a verb. Because 'anyone' is receiving the action of being blocked, it needs the را marker.

کسی usually means 'someone'. Why is it translated as 'anyone' here?

Farsi doesn't have a separate, direct translation for 'anyone' in this context. Words like کسی (someone) and چیزی (something) are used in questions and negative sentences where English naturally switches to 'anyone' or 'anything'.

Do I always need to use آیا to ask a yes/no question like this?

No, آیا is quite formal and is mostly used in writing. In everyday spoken Farsi, people usually drop آیا and just say او کسی را مسدود کرده است؟, raising their pitch at the end of the sentence to show it's a question.