pureos has 240-5pureos1 while debian has 241-7~deb10u1. One of the difference is a change of handling of drm render nodes (and the introduction of the render group). The lackof that breaks the librem5 image builds:
https://arm01.puri.sm/job/Images/job/Image%20Build/2290/consoleFull
I'll hack around that in the installer but errors in that area lead to hard to debug screen corruption so it would be great if systemd could be updated when birch is shipped.