Hi, I am facing the very same issue however, I discovered that this is a bug in plymouth version => 24.004.60-1, because if you install plymouth version 22.02.122-3 including label and themes from 'bookworm' then everything works as expected.
I can find the bug report here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1070979 Cheers, Wolf
