>Is there anything FreeBSD can do that, say, Debian cannot?

ZFS boot environments.

One could install Debian's root on ZFS by following the OpenZFS documentation guide, combine it with ZFSBootMenu (or similar), but there won't be any upstream support from the Debian project itself.

The Nitrux Linux distribution is based on Debian and provides an immutable feature similar to boot environments, but you can't treat your immutable boot images the same way you can treat your mutable data like how you can with ZFS datasets on FreeBSD.