Most method I found on the internet require the use of grub-customizer. But I did found modifying GRUB_DEFAULT in /etc/default/grub to ID>ID should do it.
I modify it to GRUB_DEFAULT=1>1, this is supposed to select second entry, and then select second sub-entry. At first boot it does work that way. But now it will select second entry then select first entry regardless what the second number in GRUB_DEFAULT is.
You can use this for the first 10 line in /etc/default/grub
GRUB_DEFAULT=saved #this will make the default the saved boot entry
GRUB_TIMEOUT=5 #this sets the time to proceed to boot
GRUB_TIMEOUT_STYLE=hidden
GRUB_DISTRIBUTOR="Manjaro"
GRUB_CMDLINE_LINUX_DEFAULT="quiet udev.log_priority=3" #this make sure you keep as you have it now
GRUB_CMDLINE_LINUX=""
# If you want to enable the save default function, uncomment the following
# line, and set GRUB_DEFAULT to saved.
GRUB_SAVEDEFAULT=true #this instructs grub to actually save the last entry you boot from
so with this method, same thing happened like last time. After I restarted and selected my boot entry, the next restart, it does choose my saved boot entry, which is First entry > Second sub-entry,
I restarted it couple of times and it works just fine.
But the next day, just like my first solution, it will choose First entry > First sub-entry, which does not boot properly anymore.
(Actually, I don’t know which sub-entry it chosen. But it’s definitely not booting properly. Only the second sub-entry, the one with initramfs that worked)
I wonder if this is a bug?
I probably should have posted my /etc/default/grub, my bad.
But I admit, I didn’t set GRUB_CMDLINE_LINUX_DEFAULT exactly like the example. I keep the default since it already had udev.log_priority=3. I wonder if that’s what causing it?
I will remove the splash apparmor=1 security=apparmor, sudo update-grub, then set my default again. If tomorrow it still works properly, I will mark this as solved.
GRUB_DEFAULT=saved
GRUB_TIMEOUT="5"
GRUB_TIMEOUT_STYLE="hidden"
GRUB_DISTRIBUTOR="Manjaro"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash apparmor=1 security=apparmor udev.log_priority=3"
GRUB_CMDLINE_LINUX=""
# If you want to enable the save default function, uncomment the following
# line, and set GRUB_DEFAULT to saved.
# GRUB_SAVEDEFAULT="false"
GRUB_SAVEDEFAULT=true
# 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"
# 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-gray/black"
GRUB_COLOR_HIGHLIGHT="green/black"
# Uncomment one of them for the gfx desired, a image background or a gfxtheme
#GRUB_BACKGROUND="/usr/share/grub/background.png"
GRUB_THEME="/usr/share/grub/themes/manjaro/theme.txt"
# Uncomment to get a beep at GRUB start
#GRUB_INIT_TUNE="480 440 1"
I am not sure if use of GRUB_DEFAULT=1>1 will work GNU GRUB Manual 2.04: Simple configuration only mentions use of a single number
so GRUB_DEFAULT=1 will boot the 2nd ‘menuentry’ which should be the fallback initramfs
for the latest installed kernel
This is not a good solution for booting later ‘menuentry’ options as the ID number is more likely to change when a kernel is added or removed
I have not seen the Advanced menu included the name, as in post by @Hagen
only simpler examples of using menuentry name, lik this: GRUB_DEFAULT="Manjaro Linux (Kernel: 5.10.7-3-MANJARO x64 - fallback initramfs)"
This is good to keep boot locked to one option, but /etc/default/grub would have to be edited when the kernel version number changes
I use the same options as @anon89812132
(GRUB_DEFAULT=saved and GRUB_SAVEDEFAULT=true)
But I add an option to GRUB to disable the Advanced menu, so It is easier to see the boot options and change which one I want to use
echo `GRUB_DISABLE_SUBMENU=true` | sudo tee --append /etc/default/grub
So I need a new way to select default grub entry to initramfs, because my laptop wont boot up with the current default grub entry.
At first boot it does work that way. 
But now it will select second entry then select first entry regardless what the second number in