is it illegal to drive with one hand in victoria

No, it isn’t specifically illegal to drive with one hand in Victoria; the law cares that you maintain proper control of the vehicle at all times.

If your one-handed heroics cause you to wander, miss signals, or fumble controls, police can book you for not being in proper control.

And if that spare hand is wrapped around a phone, that’s a separate, very illegal party you don’t want an invite to.

Best practice: two hands whenever practical, one only when necessary (shifting, operating controls) without sacrificing control—simple, safe, and less likely to attract blue and red disco lights.