@olivier if setting a EFI/UEFI partition does not work and you continue to have problems there is What to do if there is a problem installing OM Lx. The log that would be needed is the calamares-installation-log.txt that article shows user how to create.
If you have an existing EFI/UEFI partition you would use that, select mount point /boot/efi and be sure the boot flag is checked. There is no need to format an existing /boot/efi partition.