If you want to use ZFS as your root filesystem, see the Root on ZFS links below instead.

ZFS packages are included in the contrib repository. The backports repository often provides newer releases of ZFS. You can use it as follows.

Add the backports repository:

vi /etc/apt/sources.list.d/bullseye-backports.list
deb bullseye-backports main contrib
deb-src bullseye-backports main contrib
vi /etc/apt/preferences.d/90_zfs
Package: src:zfs-linux
Pin: release n=bullseye-backports
Pin-Priority: 990

Install the packages:

apt update
apt install dpkg-dev linux-headers-generic linux-image-generic
apt install zfs-dkms zfsutils-linux

Caution: If you are in a poorly configured environment (e.g. certain VM or container consoles), when apt attempts to pop up a message on first install, it may fail to notice a real console is unavailable, and instead appear to hang indefinitely. To circumvent this, you can prefix the apt install commands with DEBIAN_FRONTEND=noninteractive, like this:

DEBIAN_FRONTEND=noninteractive apt install zfs-dkms zfsutils-linux