This is my first time installing Ubuntu and using Linux so I'll try to explain everything I've done as well as state my assumptions. Please correct me if I am wrong anywhere.
I bought a laptop which came with a NVMe SSD. The default SATA mode in my BIOS (UEFI) was "RST with Optane". Now, when I first tried installing Ubuntu, I had a lot of trouble because apparently this combination (NVMe + RST with Optane) "hides" the drive. So, during the Ubuntu installation, it could not detect the disk and I could not install Ubuntu.
After following tips online, I changed the SATA mode to AHCI, which worked. Ubuntu could now detect my drive and I managed to dual boot with Windows. However, for some reason, this laptop does not work correctly when AHCI mode is set because it completely break's my laptop's sleep functionality. If I put my laptop to sleep (by closing the lid for example), it could not wake up again (both on Linux and Windows). If I opened the lid again, the screen would stay completely black (unlit) and be completely irresponsive (I tried pressing random buttons, combinations, and even tried to SSH into my laptop unsuccesfully). The fans would start back up but the laptop would not respond at all. When this would happen, I had to force shut down my laptop by holding the power button.
So I was forced to go back to "RST with Optane" mode, because for some reason the sleep function worked on that mode. So, to be able to install Ubuntu, I had to buy and add to my laptop a SATA SSD because apparently, "RST with Optane" does not hide non-NVMe drives. This worked perfectly, I was able to install Ubuntu on my SATA SSD and have Windows 10 on my NVMe SSD. However the only problem now is I cannot boot into Windows 10 from GRUB, since the inital problem of Linux not detecting the NVMe drive is still present.
So now my question is if it is possible for my GRUB to detect the NVMe drive where my Windows 10 is installed — with this specific configuration (SATA mode as "RST with Optane"). Right now if I want to choose which OS to boot into I have to use my BIOS' boot menu by pressing F12 on startup. However I'd really like to use GRUB. I was thinking of perhaps installing/moving the Ubuntu bootloader in the NVMe drive? I honestly have no idea if that would work, and if it did, would I need to completely reinstall Ubuntu? Or perhaps do the opposite, installing/moving the Windows bootloader into the SATA drive and somehow calling that from the GRUB menu?
I'm really sorry for being wordy. I wanted to explain my whole process so that hopefully, if I made a wrong assumption along the way, someone could clear that up.
Thank you so much.
TL;DR: GRUB cannot detect my Windows 10 installation because it is on a NVMe drive and my SATA mode is "RST with Optane", which apparently makes Linux not be able to detect that drive. Is it possible to make GRUB detect it, without having to change my SATA mode?