That error message looks like '4972' was accidentally added to /usr/share/initramfs-tools/hooks/plymouth. Can you restore the content of the file by reinstalling it?
sudo apt install --reinstall plymouth
That error message looks like '4972' was accidentally added to /usr/share/ initramfs- tools/hooks/ plymouth. Can you restore the content of the file by reinstalling it?
sudo apt install --reinstall plymouth