Can a portable power station run a CPAP overnight?

Yes. Most CPAP machines draw modest power, so even a ~300Wh to 1,000Wh unit can typically cover one or more nights, especially with the humidifier turned off. Larger 2,000Wh+ units add multi-night headroom. Confirm your machine's watt draw and check that the station's quiet/eco mode keeps the fan from disturbing sleep.