All the ATmega4809 I/O pins are accessible at the edge connectors on the board. The image below shows the kit pinout.
PF6 and the UPDI pin are only available at the edge connector in the debugger section as long as the cut-straps on the bottom side are not cut.
PF0 and PF1 are connected to the onboard crystal and not connected to the edge connector by default. See Section Crystal for more information.
Figure 1. ATmega4809 Curiosity Nano Pinout