RumbaMon19
Feel Pain.
Gigabyte introduced Hybrid-EFI firmware in their boards a decade ago when UEFI was not that mainstream. It’s main selling point was ability to boot off 2 TB which is limitation of MBR.
To force the firmware to behave like EFI you need to set this switch to EFI (Which you already did) and might need to manually initialize the disk (< 2TB) to GPT before installing Windows using say DISKPART. Then your Windows 64-bit OS (Windows 7 or above) should install in EFI mode with GPT partition scheme on the HDD. The firmware still remains more or less traditional BIOS with a sort small functionality of EFI introduced in it.
I had one such board and I had done extensive testing using this mode in EFI mode. Back then it was Windows 7 64 and it warned me that the BIOS may not supporting booting to this disk, I still continued and it worked with EFI & GPT actually.
Despite being Hybrid-EFI, it had basic coverage of UEFI. You could even boot to EFI Shell externally using pen drive.
One limitation on Hybrid EFI was there were no UEFI variables. There weren’t UEFI boot entries unlike full-fledged UEFI systems. You had traditional Boot menu pointing to SATA HDD1, HDD2 etc and when set to EFI, firmware was designed to just go ahead and look for Bootx64.efi at /EFI/boot folder on EFI partition, without being aware of anything else. All Windows versions capable of UEFI booting have that fallback mechanism anyways.
The firmware is deigned to switch EFI when it detects > 2 TB HDD. Else it might fall back to BIOS by default.
Also, these boards were designed back in 2010-11 when Windows 7 was mainstream, so results with Windows 10 may not be predictable, while the UEFI booting is still the same. You may need to experiment.
To test if you are actually booting in EFI or not when switch is set to EFI, try the following
Download UEFI 64 bit shell from this link edk2/Shell.efi at UDK2018 · tianocore/edk2
Rename it as Bootx64.efi. Format a pen drive to FAT32. Create /EFI/Boot folder on it and place this Bootx64.efi therein inside Boot folder. Now disconnect the HDD and see if it can boot to UEFI Shell from this pen drive. If it does, you are in fact in EFI mode.
Mouse driver is possible in UEFI but optional. Click BIOS (Again BIOS being a misnomer used by Motherboard manufactures!) is a selling point, not a must to have underlying Firmware confirm to the UEFI Specifications. With Hybrid EFI the only focus was ability to boot off > 2TB so only bare minimum EFI specs were confirmed to.
can you tell more about uefi shell and its uses? I too have it on my lappy but on clicking it says boot device not found. how to use shell and what can i change through it?