You could try to edit the /etc/default/grub and change the following line:
GRUB_TIMEOUT_STYLE='countdown'
to
GRUB_TIMEOUT_STYLE=menu
Also change:
GRUB_TIMEOUT=60
to
GRUB_TIMEOUT=-1
and run the following to update the Grub:
sudo grub-mkconfig -o /boot/grub/grub.cfg
Reboot and see if you can get back the Grub boot menu.
You could also give:
systemctl reboot --firmware-setup
a try to see if the system reboots into Bios.