Thats what I am doing right now...
I didn't have the time nor patience anymore to deal with it, my frustration was at a MAX. So I gave up, and went onto other tasks. Which I am still doing BTW.
Also, I can't keep doing endless restarts expecting different results. Eventually I just have to call it and move on, which is what I am doing now.
I think this is a problem for the Zorin brothers honestly.
Keep in mind, I also entertained the theory that maybe GRUB was getting updated for the other drive, the XFCE installation. But I checked the advanced options for Zorin OS 16 LITE, and there were no updates to it, only two kernel options listed.
This is cause I wasn't on XFCE long to allow a full list of kernels to generate. So point is, I confirmed, that GRUB was not being updated for the wrong drive. GRUB was indeed being updated for the right drive, for the right installation Zorin OS 16 Gnome.
Since there is no resolution at this time, like I said, I am moving on, I got other things to do. And I also need my computer running for other tasks, so constant rebooting into GRUB won't help me for other tasks.
I do provide you thanks for taking time out of your day, and trying to help me. But as with things in Linux, not all problems have solutions. Thats just the reality with Linux.