Should I create the Reserved BIOS boot area partition?
Solution 1:
Your problem is trying to install Ubuntu in legacy mode, instead of UEFI mode like Windows. Then you will be installing grub-efi, instead of grub-pc, and you will not need a 1M partition flagged with the grub-bios flag (needed bacause gpt partitioned disks do not have the room right after the Master Boot Block to store grub's core.img executable. Secure boot shouold not need to be turned off, unless your machine has specific problems, but if you can boot Windows with it off, it should make no difference either way.