Plymouth is the boot splash things before KDE/SDDM 's own splash screen.
You can remove and disable it if you like … its nothing but bloat.
(that would entail uninstalling the package[s], removing the plymouth entries in /etc/mkinitcpio.conf and then running sudo mkinitcpio -P && sudo update-grub)
EDIT.
Oh yeah, I forgot there would also be splash in /etc/default/grub … this should similarly be removed before running sudo update-grub.
Note: this can be replaced with quiet if you are aiming for a more ‘silent boot’.
https://wiki.archlinux.org/title/Silent_boot