Man pages matching name update-grub in section 8:

update-grub.8.en	debian 10 / grub-legacy
update-grub.8.en	debian 10 / grub2-common
update-grub.8.en	debian 11 / grub-legacy
update-grub.8.en	debian 11 / grub2-common
update-grub.8.en	debian 12 / grub-legacy
update-grub.8.en	debian 12 / grub2-common