I came knowing nothing about how to flash my Librem 5 and got some help in this thread. Then I found these instructions.
But then I got blocked when live PureOS didn’t recognize the factory wifi adapter on my spare laptop (Lenovo T460). Rather than go down that rabbit hole, I came back to my NixOS desktop and confirmed that all the relevant packages are available. I didn’t install them declaratively, just used nix-shell. Note that in order to get hardware level access to the phone, I had to run the nix-shell as sudo. This was all I needed to make the instructions work (plus git, which was already installed).
>sudo nix-shell -p python3 uuu python311Packages.tqdm python311Packages.python-jenkins