But - like almost all cars (some real recent ones are better), the output of USB means it's VERY slow charging. And if you're in a low-signal area, or the phone is busy doing other things, it might well go backward. From memory, car USBs are only about ½ an amp. If you need to charge, get a phone charger and plug it into 12 volt.
A standard USB port is rated at 500mA but I believe the ones in a 2016+ Prius are rated at 2.1A but that is shared across the 2 ports so may lead to slower charging depending on what is plugged in.
Maybe it's a regional thing - I'm fairly sure mine is only 500ma. I rarely plug my phone in - but when I did early on, I also had Bluetooth running - after ½ hour, the charge on the phone had barely changed (was still nearly empty). I did see a car with 2.1a - but from memory, it was marked "2.1" on the cover.
Those are the separate USB charging ports (the 2.1A ones). The USB port that is connected to the audio system is much lower, perhaps the 0.5A one you speak of).
This is KIA Sorento 2021 - only that lower one (front) is connected to the AUDIO - though KIA don't mention amperage, they're only for charging:
Looks like one of the three "1st row chargers" is the USB input. That's a typical setup. Again, the USB Audio input does charge but usually at a lower amperage than the dedicated charging ports.
