What does Librem/PureOS use for FDE?

If I install PureOS on a Librem with full-disk encryption, what package/module/application is used? (I’m not sure if it lives in PureOS itself or the BIOS.)

From Jonas:

FDE (Full Disk Encryption) is applied independent of boot firmware. Technically it is called “LUKS” and encryption applied to “LVM” (narrow down your searches by looking for LUKS + LVM + Debian) [1]

Your laptop loads like this:
firmware → GRUB → Linux → Initramfs → LVM → LUKS → partitions → userspace

You can check which parts of your running system is encrypted with this command in a terminal: lsblk
At the lsblk output you should be able to identify your disks (disk), conventional disk partitions (part), LUKS encryption (crypt), and LVM partitions (lvm)

[1] Helpful links (including some from Jonas):