Do you not have the "quiet" boot parameter set? What messages are you seeing before Plymouth?
In fedora 41 workstation I have a custom grub and Plymouth theme and don't see any text from kernel boot during the boot process unless I hit esc while Plymouth is on screen.
I think it was something like reflective LCD and not epaper, that's what allowed it to have a fast refresh rate but still use very little power. I'm still surprised I haven't seen much tech using that type of screen.