Boot to GRUB by default (choose OS to boot every time) [closed]

I know what key to press to boot to GRUB. But, I don't want to press any key.

I want to load the GRUB menu as my default and choose the OS each time I boot. In other words, I do not want to automatically boot one of the OS's on my computer.

How can I change /etc/default/grub to do this?

I think it can be done because once, on an old Ubuntu installation, the GRUB menu always loaded.

I'm running a dual-boot Ubuntu/Fedora.

Thanks.

Set GRUB_TIMEOUT=-1

"‘GRUB_TIMEOUT’ Boot the default entry this many seconds after the menu is displayed, unless a key is pressed. The default is ‘5’. Set to ‘0’ to boot immediately without displaying the menu, or to ‘-1’ to wait indefinitely.

If ‘GRUB_TIMEOUT_STYLE’ is set to ‘countdown’ or ‘hidden’, the timeout is instead counted before the menu is displayed."

https://www.gnu.org/software/grub/manual/grub/html_node/Simple-configuration.html