https://www.gnu.org/software/grub/manual/grub/html_node/Simple-configuration.html
https://wiki.archlinux.org/title/GRUB

info -f grub -n 'Simple configuration'

???
etc/default/grub.d

cat /etc/grub.d/40_custom
#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change

/etc/default/grub
GRUB_THEME="/usr/share/grub/themes/starfield/theme.txt"

https://microsin.net/adminstuff/xnix/nomodeset-quiet-splash-kernel-parameters.html
    https://microsin.net/adminstuff/xnix/linux-kernel-parameters.html
    https://microsin.net/adminstuff/xnix/ubuntu-nomodeset-boot-mode.html

GRUB_CMDLINE_LINUX_DEFAULT="nomodeset"
GRUB_TIMEOUT=5
# - quiet splash

ubuntu:
    sudo update-grub
other:
    grub-mkconfig -o /boot/grub/grub.cfg

generated (do not edit):
/boot/grub/grub.cfg

cat /usr/sbin/grub-mkconfig

# For full documentation of the options in this file, see:
#   info -f grub -n 'Simple configuration'