Why is the grub menu not showing up?

Question

GRUB

All necessary bootloader menu settings have been made with the choice of two OS Xubuntu and Windows 10. Both OSes are visible in the grub Customizer. Load standard selection set after 5 seconds. But when loading the menu does not appear, just a black screen and after 5 seconds the OS loads. When set to 30 seconds, it loads in 30 seconds. It turns out that there is a menu, it is formed, but it is simply not visible. What can be wrong? Windows OS was found in the customizer after editing the /etc/grub.d/custom_40 file:

#!/bin/sh
exec tail -n +3 $0
menuentry "Windows 10" {
insmod ntfs
set root='(hd1,XXXXXXXXX)'
search --no-floppy --fs-uuid --set XXXXXXXXX
chainloader +1
}

Here, as far as I understand, hd1 means the second hard drive? But after the command,
sudo update-grub
this file completely disappeared. The system finds Windows in the customizer, but does not find it in the terminal after update-grub. When you re-create the file and enter this command, the same thing, again the file has evaporated. But the system finds Windows in the customizer, but does not find it in the terminal after update-grub. Can you explain what is actually happening? sudo os-prober doesn't help

Answer 1

The menu appears when you press Esc once. In order for the menu to appear by default without keystrokes, you need to set the option in /etc/default/grub:
GRUB_TIMEOUT_STYLE="menu"
and then
sudo update-grub