I’m probably mistaken, but I think there might actually be a plugin for this? I haven’t looked into it myself but I swear I scrolled past a plugin listing similar functionality at some point. Or I could be hallucinating. Or it could even exist but no longer work on the current version of the app. Who knows!?

The bazzite project website has an explicit “how-to” for extra drives. Worked for me with no issues, though I am definitely more experienced with tinkering with that kind of thing.

Bazzite would be my suggestion. Throw the full install on the ssd then format the HDD for general storage. I’d be a little concerned about the 1060 3GB GPU though. Drivers will likely be fine, but the “10 series” have notoriously awful async compute and take a much larger penalty when running games/apps under proton/vulkan if I recall correctly.