I have the Terra C (carbon version). The geometry and max tyre width definitely make the Terra C much more gravel oriented than the Terra G. However, the build quality is excellent, and I can't imagine the Terra G will be any different. And with a 35mm tyre clearance, you should be able to conquer a bit of light off-road. The Terra C replaced a Felt CX bike that was stolen. It also had a 35mm tyre clearance, and I took it on mtb trails, singletrack, gravel fire roads, etc and it coped for the most part (unless muddy).
If you did want to make the Terra G a bit more capable off road, a second set of knobbly 35mm tyres and swapping out the chainrings to 46/30 is doable, and wouldn't be too expensive if you can do the work yourself. The only bike available immediately in my size was the Terra C, and it was the more road oriented version (full 105, with compact 50/34 chainrings), and 32mm road tyres. By sheer luck, my felt was recovered, although the frame was trashed. However, I was able to knab the 46/30 chainset and wheels (which I had upgraded from stock) off of it. So I put a set of 40mm knobblies on the stock Orro wheels and swapped out the 105 chainset for the FSA 46/30 chainset from my felt. My old felt wheels already had a set of 32mm Pirelli Cinturato Velos for commuting on them so kept that set of wheels for road riding. It is a brilliant machine off-road, and equally brilliant on road.
Pic below at the start of my bikepacking trip last summer.
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