Try it with full disk encryption or any sort of partition encryption which requires passwd input during grub loading, in my part I have rootfs encrpted with luks+lvm, /home partition encypted with luks and some automated unlock process:
First, the password input interface before plymouth animation is currently as ugly as you can imagine, and even fonts error since I’m Chinese… I know that’s not handled by plymouth but the grub module and password interface should be modified as well, at least more modern-like. As far as I know once your disk is encrypted, there will be a seperate /boot partition without the lvm group, which means easy modification.
Second, it just FAILs to display the plymouth animation and GDM login interface after I entered my password and unlocked the disks, unless I press a key while regular systemd startup process, which activate the cli mode or press again to change back to plymouth , this is annoying.
Third, GDM background should be redesign to match the conception of flicker-free boot, maybe some color gradient like in Macos.