What a nightmare.
The end result is a working Manjaro at least. Two of them in fact! One installed on a /dev/sdb and another on a /dev/sdc! How?? Why? Well, I shall tell the tale.
Anyone who has Windows 10 installed on a 'clean' storage device and attempts duel-boot with a linux OS will know that they are going to have a bad time. Espeically if they had Windows installed with U/EFI, which is what I had. I attempted to install Manjaro with GRUB on a EFI...
Hmm... I am willing to admit that I am not a big Linux nerd, so it makes sense that I am not a big GRUB nerd either; I knew of UEFI/EFI due to past experiences when trying to install Manjaro on a different computer. How do I put this... Lenovo really could have done a better job with the UEFI menu. When you deleted the 'secure keys' you had to boot into Win10 and then shutdown and start the laptop with that Lenovo button and then MAKE SURE YOU BOOT INTO THE MENU AND NOT SOMETHING ELSE BECAUSE IF YOU MISS CLICK, WHICH WAS VERY EASY TO DO, YOU HAVE TO RESTART THE WHOLE THING AGAIN BECAUSE LENOVO DIDNT THINK TO PUT A 'BACK' OPTION and then disable the 'secure boot' and then boot into Win10 again so the settings could save (deleting the keys leaves the 'secure boot' toggle greyed out without booting into Win10 first for some reason) and then you can boot from a non-windows install on the laptop! 😠
I was this close
This is my experience with UEFI the first time I encountered it. Lets just say it took 'a while' to figure out that you need to boot into Win10 to have that secure boot option toggleable. Also, I don't know why but they put a 32bit bootchip thing on a 64bit laptop... Most (every single one I tried) distros had 64bit boot-thing paired with 64bit OS... not 32bit boot-thing paired with 64bit OS which was a 'fun' puzzle to solve. I actually never would have solved that puzzle without the Manjaro community. Without the Manjaro community that laptop would have been still using Win10. The Ideapad 100s... Lenovo really did a number on me. They also cemented permanate negative feelings towards the characters 'UEFI'. Even though UEFI is technically better than BIOS (or so I've read), I still harbor residual rage. Next time I buy a laptop it won't be from Lenovo and it will not have UEFI.
I had a better experience with this attempt... even if it did take me like 8 hours to 'solve.' When using the install-'cd'-icon that Manjaro offers, it would always fail at the bootloader part. I could never get it to work. I wanted to just install it and be done, like in the good old days with BIOS. Well, it turns out that I was 'live-cd'-ed into 'legacy' which meant BIOS but of course I did not know this and when I went to install the OS... Well Grub always failed like I mentioned. So, I followed every single piece of instructions that I could; sudo update-grub, one that made you chroot into the installed Manjaro then updated grub but first made sure you had some tools like dosfstools, mstools, efibootmgr... I remember having to see what an efi related command did but I got a fun error message: EFI variables are not supported on this system. :) Anyway, this means that the live-CD was not booted in EFI mode. It turns out my motherboard can do both UEFI and legacy(BIOS). So, not knowing this is my fault. I go to restart my computer and didn't press the del key enough times and then grub appears. With two options for Manjaro. Yes! Exactly what I wanted! But no options for Windows... No biggie; I'll just make a GRUB entry for the window EFI bootloader and it'll be ok! Long story short, legacy GRUB does not like EFI and I am unsure if EFI Grub likes legacy and frankly I do not want to know. When I want to switch between Linux and Windows, I go to the motherboard's "UEFI BIOS" (by pressing the del key enough times) and I switch every boot option to either Legacy only or UEFI only and manually boot into the correct drive. While disgusting, it works. Technically, I did not manage to install an OS with UEFI, but clearly that was my fault for not making sure I was in EFI mode. This whole thing was too nasty for me, so I will try to stick with motherboards with only BIOS from now on even though in this case my issues were self-inflicted.
Also, there is something that people who want to duel-boot with Windows 10 should know: cmd with admin privs --> powercfg -h off This turns off the 'hibernation' mode..... meaning when you turn off your computer the OS actually shuts down- not leaving the harddrive/ssd in somekind of hibernation state. I was able to mount the hibernation drives but only as read-only. Also disable fast boot. Otherwise, from my understanding, GRUB will not pick up Win10 and you will have a lot of 'fun' puzzles to solve.