You might choose to setup Ubuntu 22.04 LTS on your Librem14 as of today, as it should offer several advantages over current stable ones.
Also, after inserting some empty 4GB+ USB flash drive within PureOS Terminal please execute:
sudo fdisk --list −− in order to get correct address of mounted USB flash drive (/dev/sdX is probably /dev/sda but still needs to be confirmed as such)
cd /jammy-desktop-amd64_download_folder
sudo fdisk --list /dev/sdX
sudo dd if=jammy-desktop-amd64.iso of=/dev/sdX
sudo fdisk --list /dev/sdX −− check if USB flash drive ready as setup media.
Now you can poweroff your PureOS and proceed …