Again: the FX6 is a great bike; with suitable tires, it will be just fine on non-technical unpaved surfaces: dirt and/or gravel roads and tracks, including forest tracks and bridleways/towpaths and the like.

The Checkpoint is a 'gravel' bike, yes, but essentially one can think of 'gravel' bikes as 'hybrids' with drop bars. So the same points apply: a Checkpoint would be just fine on all the surfaces that an FX6 would be -- again, with suitable tires.

However, as another poster points out indirectly, if by "off-road" you mean more technical singletrack/mtb trails -- different story. Very skilled/physically-resilient cyclists can and do ride those on hybrid/cyclocross/'gravel' bikes, but at 68 I certainly wouldn't and don't. I love mtb'ing, but I have a mountainbike for that.

So really only you can decide what will work for you. My advice: try some different bikes/types of bike, and purchase now what you think will work for what you think the bulk of your riding will be now. You can always add another one later.

I will say one thing: the notion that a bicycle like an FX6 is somehow inherently prone to spilling you if it hits a bit of dirt, sand, or gravel is nonsense. As I said in my first post here, I've been riding a Specialized Sirrus on slick 32mm 'road' tires (see pic below) on the kinds of mixed surfaces you mention in your original post, and on wet, slick Autumn leaves each year, for years. I now have a new one, but the point remains: never been an issue.

Good luck!