Hide grub menu on boot

This is controlled by grub env variable menu_auto_hide. You can check what it is set to with:

sudo grub2-editenv - list

To hide menu you can set it with:

sudo grub2-editenv - set menu_auto_hide=1

To show menu:

sudo grub2-editenv - unset menu_auto_hide

The - in this command means use default filename /boot/grub2/grubenv

grub will only hide the boot menu if flag boot_success is set.If for one or other reason flag is not set it will show menu on next boot.
You can force this flag with:

sudo grub2-set-bootflag boot_success