solus defaults (if yr bios shell is not legacy) to an efi (uefi) boot format when it installs its own non-grub bootloader. don't know where the idea came from to use solus live to recover another OS's grub loader? Solus live is being mentioned as a tool in these two posts, as I read them, and not something you have installed already?
I just did the opposite and forced grub Ubuntu to install on a gpt partion with solus already there. Surpsingly it made two boot entires: a grub for itself and a uefi for itself. It's a dual boot and I always pick the UEFI.
trying to see if something this outside the box would help Rallebiker and Frank-Starr ?
a screenshot of your gparted partitons may be revealing and may help someone to help you
