Something happened in the last months. Whenever I upgrade, it seems like
the os-prober part is disabled. This is just PITA. I can use the usual:

dpkg-reconfigure -plow grub-efi-amd64

... to turn it back on, and after an upgrade it's lost again. WHY?

Now I started seeing messages after installing a new kernel package:

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.
Adding boot menu entry for UEFI Firmware Settings ...

Sorry, dear maintainer, WHAT DOES THAT MEAN? Which documentation? From
which package? Why does this reset my settings?

Best regards,
Eduard.