Have you actually tried setting GRUB_HIDDEN_TIMEOUT=0 in /etc/default/grub? I haven't tested it, but the documentation [1] seems to imply that if set to 0 it will disable displaying the grub menu. The value is only non-zero by default if os-prober finds another OS but it looks like the user is free to change it. Make sure to run update-grub after though.
Have you actually tried setting GRUB_HIDDEN_ TIMEOUT= 0 in /etc/default/grub? I haven't tested it, but the documentation [1] seems to imply that if set to 0 it will disable displaying the grub menu. The value is only non-zero by default if os-prober finds another OS but it looks like the user is free to change it. Make sure to run update-grub after though.
[1] https:/ /wiki.ubuntu. com/Grub2