5.16. How can I give init write access to /etc/initrunlvl so LIDS doesn't complain about it during startup and shutdown?

Unfortunately, there isn't much you can do about this. Because init recreates this file each time you boot, it will have a different inode number every time. This makes it difficult for LIDS to handle. It is a harmless error, and your system will still function properly without /etc/initrunlvl.