This is using GPT partition layout and UEFI boot. I had Debian 12 and Opensuse dual booting, with Debian 12 having its own Grub, and opensuse having its own grub, so I could choose which system from the UEFI ? firmware settings on grub.
Then I installed a new system running Debian 13. During the installation it installed grub, but afterwards I could not find Debian 12 anymore. My attempts to re-install grub didn't work well and I ended up with only Debian 13 booting without any grub menu, or opensuse booting with grub. I had to in the end use the usb rescue system to re-install grub from the Debian 12 system. Why did this all go so wrong? Why would Debian 13 boot without displaying Grub, even though it had a timeout of 5 seconds?
