Possibly related info: Lenovo Legion-Y540. Windows was installed first. Ubuntu couldn't detect any other OS while installing using the .iso on a bootable USB device too.
Firstly, I literally have no idea about how Operating Systems work at lower levels and anything related to them. Plus, I have almost no experience in any sort of UNIX system. I have installed Ubuntu on my computer on a particular partition on my SSD, assuming that I could dual boot. Now I have this problem:
I have only 1 element in Boot Section for UEFI that is not Network related, which starts with "Windows Boot Manager". Fast start-up and secure boot are disabled.
If I boot my computer giving UEFI top priority, Windows boots and pressing shift wouldn't trigger GRUB.
If I boot my computer enabling Legacy Support and giving it's elements top priority, I can access either to GRUB or to Ubuntu, but on the list there's no Windows.
I need some insight, thanks!