Don’t do this.
You need to do it as root, so the sudo at the start of the command is correct. Why it’s not working is another story.
An alternative would be to enter a super user shell (at least according to me 
), aka root shell,
su
Then enter your root password.
When successfully in the shell, edit the /etc/default/grub file with a text editor, nano in this case:
nano /etc/default/grub
Scroll to the bottom and insert:
GRUB_DISABLE_OS_PROBER=false
Save and exit.
Once back in the command line, still as root run:
update-grub
If successful, pray for the best, hold your thumbs - not that tight - and reboot.
This should get you your grub back. If not, I’m innocent and not here.