Ah it's because the new systemd (which will fix this) is stuck in proposed. To work around it you need to manually revert:
https://launchpadlibrarian.net/709437063/plymouth_23.360.11-0ubuntu1_23.360.11-0ubuntu2.diff.gz ** Changed in: plymouth (Ubuntu) Status: New => In Progress ** Also affects: systemd (Ubuntu) Importance: Undecided Status: New ** Changed in: systemd (Ubuntu) Status: New => Fix Committed ** Changed in: plymouth (Ubuntu) Status: In Progress => Won't Fix -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/2051765 Title: Plymouth FTBFS (even after apt-get build-dep plymouth) Status in plymouth package in Ubuntu: Won't Fix Status in systemd package in Ubuntu: Fix Committed Bug description: dh_install dh_install: warning: Cannot find (any matches for) "lib/systemd/system" (tried in ., debian/tmp) dh_install: warning: plymouth missing files: lib/systemd/system dh_install: error: missing files, aborting To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/plymouth/+bug/2051765/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp