Multiple windows drive icons when starting with alt: sadly the default one is failing

I'm fed up with being always force to press the alt button when I want to start windows while it should be my default OS.

The default one leads to a black screen. The other one start Windows 10 in bios mode with no trouble.

As far as I read, I suppose it's a problem with the files on the EFI boot partition. But I never managed to correct it.

From Mac, I can mount and see both partition EFI & Bootcamp. From Windows I don't manage to mount /dev/disk0s1 with diskpart (no filesystem) and I'm not sure anyway what commands I should use.

My iMac is late 2013 with a GeForce GT750M, said to have better 3D support in Windows when started in BIOS mode.

It used to work normaly before I moved the BOOTCAMP partition. Then with gdsik I cleaned my partition, and with a USB windows I corrected the boot trouble leading to this second drive icon: Nice to boot again, but a bit boring with time.

Regards,