I recently had Linux Mint installed alongside Windows 10, and GRUB listed both of them with no issues. I then decided to try out Ubuntu 19.10, and installed it at the same partition as Linux Mint (letting the installer wipe and replace that partition in the process). After all was said and done, GRUB would only list Ubuntu. I’ve so far tried sudo update-grub, with no luck. As well, I tried os-prober (with sda mounted, the drive with Windows 10 installed), and listed no output. If I try boot-repair, it gives me the “GPT detected” error, but I’m unsure how exactly to fix that.
Here’s my boot-repair log: https://paste.ubuntu.com/p/4tx2d9tGGv
I’ve not found a way to boot back into my Windows 10 install at all, so I’ve not been able to try any repair options on that side.