Certainly old news for some, but a pleasant surprise for me... #Purism has made reflashing #PureOS on the #Librem5 with LUKS encryption ridiculously easy. Just put the phone in flash mode and run these 4 commands in Terminal:
sudo apt install git python3-jenkins python3-tqdm uuu
git clone https://source.puri.sm/Librem5/librem5-flash-image.git
cd librem5-flash-image
sudo ./scripts/librem5-flash-image
Set the LUKS passphrase on first boot, change the user password, and you're off!