Mount filesystems

Mount root first, substituting the root partition you created:

mount /dev/nvme0n1p2 /mnt

For UEFI, mount the EFI system partition at /boot inside the new system:

mount --mkdir /dev/nvme0n1p1 /mnt/boot

For BIOS, skip the ESP mount. If you created a separate home partition, mount it at /mnt/home using mount --mkdir and its actual device.

Check the result before installing:

findmnt -R /mnt

On UEFI, /mnt/boot must be mounted before pacstrap so the kernel and initramfs are written to the ESP.