Solus does not use Grub assuming you are using EFI. Solus uses clr-boot-manager. If you are using a BIOS based board then sudo grub-mkconfig -o /boot/grub/grub.

What file system does Solus use?

Mounting your system

Whether you're using GRUB or UEFI, you will need to mount your Solus root ( / ) partition as the first step of performing a boot rescue. This is typically your primary partition, formatted as the filesystem type ext4 .

Is GRUB boot loader necessary?

The UEFI firmware ("BIOS") can load the kernel, and the kernel can set itself up in memory and start running. The firmware also contains a boot manager, but you can install an alternative simple boot manager like systemd-boot. In short: there is simply no need for GRUB on a modern system.