I had a look at your videos and noted that when looking at the boot options, the BIOS only offers the ct500p155d8 disk (be it windows or elive entry) .... which is your nvme drive. This a boot order thingy.
Iḿ not totally in the clear on your setup but you definitely need to make clear in the bios/firmware settings that it needs to boot from your sata disk (ct500d37124) as the entries on your nvme are clearly a mess. From what I see Grub-install saw your windows on the nvme and added that to the menu choices on the sata so it shouldn't be a problem keeping it as your first boot device.
Is this desktop machine or a laptop i.e could it be that both sda and sdb are external USB disks?
That could create certain boot problems depending on the geotmetry of those disks.
Like I mentioned before, I´m sure that the GrubBootdisk will suffice to start the installed system but wouldn´t solve your problem unless you're prepared to do some commandline voodo with "efibootmgr" or install "refind" to tweak your efi files.... or use their provided boot-disk:
The issue is clearly that your BIOS startup needs changing and/or the efi files on the nvme need tweaking.
The Elive installation ran perfectly but your machine doesn't boot as wanted which is down to your Bios settings.