Hello paxmark2,
plain debian systems support mounting /usr from the initramfs,
so the issue applies to systems that don't use an initrd (e.g. mips).
The siduction installer doesn't suggest a separate /usr partition.
The changelog of systemd 230-5 mentions #828991
* debian/rules: Ignore libcap-ng.so in the "does anything link against /usr"
check, to work around libaudit1 recently gaining a new dependency against
that library (#828991). We have no influence on that ourselves. This fixes
the FTBFS in the meantime.
so the dependency is gracefully ignored
greetings
musca