Yes, with the car in a special V2L or "utility" mode rather than fully off.

The drivetrain is off, but the high-voltage system stays active to power the inverter and the socket. On most models you activate V2L from the infotainment screen or via a button. Most vehicles disable V2L automatically once the car is shifted into drive, though behaviour varies by model: some cars allow cabin sockets to keep working while driving, others disable only the external port. The car will also shut V2L off when the battery hits the reserve threshold, usually 15 to 20%.