Am Samstag, 14. September 2019 schrieb Ralph Ronnquist via Dng:
> That same question apparently came up a while ago at
> https://unix.stackexchange.com/questions/56004/how-to-stop-update-gru
>b-from-scanning-all-drives
>
> In short: do something to /etc/grub.d/30_os-prober
> (which is a shell script)

Maybe even easier is to edit /etc/default/grub:

# Normally, `grub-mkconfig' will try to use the external `os-prober'
# program, if installed, to discover other operating systems
# installed on the same system and generate appropriate menu entries
# for them. Set this option to `true' to disable this.
GRUB_DISABLE_OS_PROBER=true

# List of space-separated FS UUIDs of filesystems to be ignored from
# os-prober output. Mit "@/dev/sdx" funktioniert es endlich.
#GRUB_OS_PROBER_SKIP_LIST=b8123ca5-5c39-49c5-ac51-0bc73c72e0d9@/dev/sdb5

HTH

Kind regards,
Stefan