GRUB submenu can be navigated with the keyboard however it does not show on the display and what was there on the screen before the grub menu loaded shows instead.
With a bit of trail and error I figured it out but to test my hypothesis, I selected the endeavourOS from my UEFI boot entries. When I had installed Endeavour, I had setup timeshift autosnap with Grub-BTRFS with the guidance of the EOS discovery wiki page on it.
Here are the contents of /etc/default/grub
which I had modified before to suit my tastes
# GRUB boot loader configuration
GRUB_DEFAULT='0'
GRUB_TIMEOUT='5'
GRUB_DISTRIBUTOR='EndeavourOS'
GRUB_CMDLINE_LINUX_DEFAULT='psmouse.synaptics_intertouch=0 nowatchdog nvme_load=YES resume=UUID=dda3f538-bb25-4bfb-9915-d64b5f460ba8 loglevel=3'
GRUB_CMDLINE_LINUX=""
# Preload both GPT and MBR modules so that they are not missed
GRUB_PRELOAD_MODULES="part_gpt part_msdos"
# Uncomment to enable booting from LUKS encrypted devices
#GRUB_ENABLE_CRYPTODISK=y
# Set to 'countdown' or 'hidden' to change timeout behavior,
# press ESC key to display menu.
#GRUB_TIMEOUT_STYLE=menu
# Uncomment to use basic console
GRUB_TERMINAL_INPUT=console
# Uncomment to disable graphical terminal
#GRUB_TERMINAL_OUTPUT=console
# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `videoinfo'
GRUB_GFXMODE=auto
# Uncomment to allow the kernel use the same resolution used by grub
GRUB_GFXPAYLOAD_LINUX=keep
# Uncomment if you want GRUB to pass to the Linux kernel the old parameter
# format "root=/dev/xxx" instead of "root=/dev/disk/by-uuid/xxx"
#GRUB_DISABLE_LINUX_UUID=true
# Uncomment to disable generation of recovery mode menu entries
GRUB_DISABLE_RECOVERY='true'
# Uncomment and set to the desired menu colors. Used by normal and wallpaper
# modes only. Entries specified as foreground/background.
#GRUB_COLOR_NORMAL="light-blue/black"
#GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
# Uncomment one of them for the gfx desired, a image background or a gfxtheme
GRUB_BACKGROUND='/usr/share/endeavouros/splash.png'
#GRUB_THEME="/path/to/gfxtheme"
# Uncomment to get a beep at GRUB start
#GRUB_INIT_TUNE="480 440 1"
# Uncomment to make GRUB remember the last selection. This requires
# setting 'GRUB_DEFAULT=saved' above.
#GRUB_SAVEDEFAULT=true
# Uncomment to disable submenus in boot menu
GRUB_DISABLE_SUBMENU='false'
# Probing for other operating systems is disabled for security reasons. Read
# documentation on GRUB_DISABLE_OS_PROBER, if still want to enable this
# functionality install os-prober and uncomment to detect and include other
# operating systems.
#GRUB_DISABLE_OS_PROBER=false
Here’s the output of sudo fdisk -l
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: ST1000LM024 HN-M
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 48A93804-3E37-4500-AAD9-E444F8F009D4
Device Start End Sectors Size Type
/dev/sda1 4096 2052095 2048000 1000M EFI System
/dev/sda2 2052096 1935065087 1933012992 921.7G Linux filesystem
/dev/sda3 1935065127 1953520064 18454938 8.8G Linux swap
Partition 3 does not start on physical sector boundary.
I have tried holding down esc during boot or pressing any key during boot. I also removed quiet and splash (splash I had added previously to use plymouth)
Thanks in advance for the answers !