seeking how to GRUB multiple drives with menu

Can someone help me sort out a GRUB/GRUB2 issue with my laptop?

I did a fresh install to the internal HDD and wrote the boot to its
/dev/sda. The system only boots if I have both HDD drives installed.
If I remove the bay drive, boot fails with various errors.

Since /dev/sda is self contained complete install, I believe that I should be able to enable all three drives to boot.

• all drive show a grub menu to boot all drives
• SDD the primary source of boot for the speed advantages. Might also contain "root" folders and files used during boot as recovery option
• /dev/sda also bootable and holding all of the end-user and assorted folders and files.
• BAY also bootable

I have an internal HDD and an internal SSD. In addition, I have a dockiing station (port replicator) that has an HDD in a removable drive bay. This drive is not hot-swap.

I'm running Mint v21.3 with Cinnammon on the internal drive.
I have Mint 21.2 on the drive bay.
The box is supposed to boot from the SSD, but does not.