Yes, this fix https://salsa.debian.org/kernel-team/initramfs-tools/merge_requests/23/diffs indeed at least silenced (maybe fixed) those wornings after update-initramfs -u
Hope you will pull that in initramfs-tools-core as shown by dpkg -S ./mkinitramfs And *I hope* it will happen faster than with this obnoxious bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=931930
