Why did Octavian declare war on Cleopatra rather than directly on Mark Antony?

Octavian declared war against Cleopatra rather than Mark Antony primarily as a strategic move in a sophisticated propaganda war.123

By framing the conflict as a war against a foreign queen, Octavian avoided the appearance of initiating a civil war against a fellow Roman citizen, which would have been politically damaging. Instead, he successfully portrayed Antony as a man who had been manipulated by Cleopatra and was sacrificing Roman interests to serve her ambitions. Octavian used this narrative to convince the Roman public and the Senate that Antony intended to transfer the capital of the Roman world to Alexandria and rule as a Hellenistic monarch.1324

This approach allowed Octavian to consolidate support across the West, forcing Roman elites to choose between loyalty to Rome and allegiance to a foreign power. By declaring war on Cleopatra, he effectively cast the struggle as a patriotic defense of Rome against an external threat, rather than a personal power struggle between two Roman leaders.231