the full error message at the end of update-grub: Warning: os-prober will not be executed to detect other bootable partitions. Systems on them will not be added to the GRUB boot configuration. Check GRUB_DISABLE_OS_PROBER documentation entry.
Question: why would this desirable? it's totally new to me. Back story: I just upgraded a Bullseye install to Sid. this is a multi-boot machine, my daily driver is Bullseye. after reboot my GRUB had only one entry I was able to get it back (thanks to Google) edit /etc/default/grub add GRUB_DISABLE_OS_PROBER=false saved then ran grub-install /dev/sd(foo) && update-grub
