The 2 USB ports are only “live” when the ignition is switched on. However, I’ve noticed that after the ignition is switched off, they remain live for about 90 seconds. Oddly though, when I unlock the driver’s door, the usb ports become “live” straightaway briefly. Also I’ve noticed that they become “live” if, after I’ve switched the ignition off, and waited for a few minutes in the car then opened the driver’s door, they become “live” briefly.  Not an issue, but curious why this is happening.

A non-technical explanation...

When the driver's door is opened, the car thinks it likely that it will be driven and runs a 'boot up and check' routine that causes the USB ports to become briefly live despite the car's ignition not being switched on. If the ignition is then switched on, the USB ports become continuously live.

When the ignition is switched off, the car begins to shut down non-essential items like the USB ports but the shut isn't instant.

The driver's door is 'important' to a Fabia Mk4 - for instance, if the car has a starter-button, the Owner's Manual advises that, when replacing a fuse, the car's ignition must be switched off and the driver's door open.

(Of course the behaviour could be down to the tiny malicious demon that Skoda has imprisoned in the electronics of all cars built since 2020.)