My suspicion is that your problem is not related to Secure Boot. Ubuntu, which you say you installed, supports Secure Boot. So do Fedora, OpenSUSE, ALT, and several others. That said, there are known problems, mostly with flaky EFIs; but these problems would normally prevent the installation medium from booting, so you wouldn't have gotten as far as you have if Secure Boot were the problem.
Your boot options screen doesn't show an entry for Ubuntu, which suggests another problem: Something went wrong with your boot loader installation. You should be able to launch the Ubuntu installer, but select the "try before installing" option, in order to investigate. The Linux
efibootmgr command lets you set boot loader options. There are several tutorials and references on this command on the Internet, but I know of none that's really ideal for your circumstances. Still, you might want to read:
Also, keep in mind that your boot loader is probably already installed to the EFI System Partition (ESP), which is a FAT partition that's probably the first or second one on your disk. The Ubuntu boot loader should be
EFI/ubuntu/grubx64.efi on that partition; however, to work with Secure Boot, GRUB must be launched by a program called Shim (
shimx64.efi, normally). Thus, to create an entry for GRUB with
efibootmgr, you'd refer to Shim, as in:
sudo efibootmgr -c -d /dev/sda -p 1 -l \\EFI\\ubuntu\\shimx64.efi -L "ubuntu"
This should create an entry, although you may need to adjust some details. Several things can go wrong with this, though, and one of them may explain your problem:
- If the installer couldn't write the files to the ESP, the entry created by
efibootmgr will be useless. Such a problem could happen because of improper partitioning (particularly if you manually partitioned and didn't know you had to create an ESP), because of a random disk error, etc. If this is the source of your problem, you'll need to use something like Boot Repair to re-install GRUB.
- Some EFIs have bugs that cause them to "forget" or ignore the entries created by
efibootmgr. If this happens, you may be able to create an entry, but there will be no trace of it when you reboot. This problem is best dealt with by replacing the faulty computer, but awkward workarounds involving renaming the boot loader will work if this isn't possible. Lenovos don't normally suffer from this problem, fortunately.
- Removing a disk and powering on the computer sometimes causes NVRAM entries for no-longer-valid entries to disappear. This is probably intended as a helpful feature, but it's a pain if you regularly unplug your disks for any reason. This is unlikely to be a factor for your laptop, but I thought I'd mention it anyhow.
To more directly answer your question, Secure Boot is disabled in the firmware, not in Windows. (In fact, if you could disable it from Windows, that would defeat the point of it, since malware would just do it that way.) Details vary greatly from one computer to another, so it's hard to provide step-by-step instructions. Nonetheless, I provide such instructions for four systems on this page. With any luck, your system will be similar to one of them, should you actually need to do this.