I just recently installed Solus on a separate SSD from my Windows 10 drive. When I installed Solus, I disconnected all other drives from my computer (including the Win10 drive). Now, when I get to the boot loader, I have the option to boot to Solus but not Win10. How can I get Win10 to appear in the boot loader?

You need to enter your BIOS boot loader. Press Esc, F2, F8, or F12 its depends on your machine. Then you can choose Windows to boot Windows 10 or choose Linux Boot Manager to boot Solus. You can also change the default from your BIOS.

Do I have to go to the BIOS every time I want to switch the OS? Is there no way to use a Grub style boot loader?

    You may be able to add it by running 'clr-boot-manager update'
    It would have been automatically done for you, if you hadn't disconnected the drive during installation.

    We're assuming this is EFI. Please take a picture of the menu that allows you to boot Solus.

    Grub, can be updated by running 'update-grub' as root, and should detect and add Windows as boot option.

    @dbarron When I run 'update-grub' I get this message, and when I reboot there are no new options in the grub menu. root@solus-pc /home/xxx # update-grub
    Generating grub configuration file ...
    WARNING: Failed to connect to lvmetad. Falling back to device scanning.
    done