I guess you install the dual system by the way of advanced installation. If your BIOS is in EFI mode during the advanced installation, we must first divide the disk into an EFI partition, then do a swap partition, and finally allocate a root partition. The partition of EFI partition can be completed by referring to the following figure:
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During the installation, I have the following message:
"The /boot boot partition must be a primary partition ant the first partition on the disk"
I always had Windows on the first partition and I don't want to uninstall it.
Please remove this limitation from the final version.