To show the GRUB menu in Fedora, use the following:
sudo grub2-editenv - unset menu_auto_hide
# OR
sudo grub2-editenv - set menu_auto_hide=2
Then regenerate your grub configuration:
sudo grub2-mkconfig -o /etc/grub2-efi.cfg
To hide it again:
sudo grub2-editenv - set menu_auto_hide=1
sudo grub2-mkconfig -o /etc/grub2-efi.cfg