Your bike is fine for gravel.
As I recall, you can put something close to 45mm on that bike. Take out the ruler, and see what she says. 40mm should work easily. Personally, 40mm is fine for anything that isn’t a fast downhill single-track with rocks and roots. There are lots of gravel options in the 35-40mm range.

I have the specialized version of that bike in my stable. It basically has mountain bike geometry, but isn’t quite as overbuilt as a mountain bike (and won’t take 60mm wide tires). That style is more of a gravel or a mountain bike than a road bike.

Tires are big factor. If you can go tubeless and get down to around 30psi (40mm tires) you should be fine on any rail trail.