What should I do exactly?
If anyone is interested, I can provide the pastebin link which boot-repair has generated
Below the final file part
=================== Repair blockers GPT detected. Please create a BIOS-Boot partition (>1MB, unformatted filesystem, bios_grub flag). This can be performed via tools such as Gparted. Then try again. Alternatively, you can retry after activating the [Separate /boot/efi partition:] option. =================== Advice displayed in case of recommended repair EFI detected. You may want to retry after activating the [Separate /boot/efi partition:] option. Do you want to continue? =================== Final advice in case of recommended repair Please do not forget to make your BIOS boot on sda (1000GB) disk! =================== Default settings Recommended-Repair This setting would purge (in order to fix packages) and reinstall the grub2 of sda2 into the MBRs of all disks (except USB without OS). Grub-efi would not be selected by default because: no-win-efi Additional repair would be performed: unhide-bootmenu-10s fix-windows-boot =================== Settings chosen by the user Boot-Info This setting will not act on the MBR. No change has been performed on your computer. See you soon!