Felix Miata composed on 2021-08-19 18:11 (UTC-0400):
grep GRUB_DISTRIBUTOR= (on/from both sda1 and sdc1) grep GRUB_DISABLE_OS_PROBER= (on/from both sda1 and sdc1)
I left out the file to grep:
/etc/default/grub
e.g.
grep GRUB_DISTRIBUTOR= /etc/default/grub