running zorin 10 off HDD, cannot boot into zorin 9 lite usb

I'm running zorin 10 and was in error when I thought it was the newer/longer-supported version.

I have zorin 9 lite installed on a USB3 stick. It's a spartan GUI but wow it's fast.

My problem: I can't boot into the OS on usb from here. It works just fine on the windows PC though. "Try Zorin without installing" and I'm right into the OS.

But installed HDD zorin OS trying to boot into zorin OS on usb, well that's just not jiving for some reason.

HDD has a few pre-fail status in the disk testing tool I used here. So I need to start using/working from the USB before I lose this drive completely.

Other hardware is fine, just can't afford to have (or replace) a crashed HDD.

Suggestions? I can save my Zorin files, install Ubuntu fresh, then boot into the USB? That'd work?

(tips/advice about using Zorin OS from usb as primary and portable "workspace" appreciated as well)

Apologies for double post but a quick thought: would disabling the HDD altogether in bios then simply booting into USB work?

I'm too afraid to try something as drastic as that (to me anyway) without an answer though.