Ah, turns out I need to add "GRUB_DISABLE_OS_PROBER=false" in /etc/default/grub. I think it is bad to silently change the default in an upgrade here, since it can leave people locked out of an OS they need. GRUB_DISABLE_OS_PROBER is not even listed in /etc/default/grub.ucf-dist. Kind regards, Ralf