>>1493259In theory, yes, there might be differences. Typical differences may include
- less tire clearance on cx bike
- steeper headtube and seattube angle
- lower stack to reach
- higher bottom bracket
- shorter chainstays
- cx-specific crankset, e. g. 46-36
- closer-ratio cassette
- less or no mounting points for racks and fenders, as you already said
- flattened top tube or other gimmicky stuff to facilitate carrying the bike
- [...]?
To be fair, in practice, the difference is often pretty negligible. There's cx bikes with compact cranksets, rather low bb's, mounting points, quite comfy geo, ample tire clearance...
I ride a Cube Cross Race SL (2019), which is Cube's cx offering. However, except for the less sloping top tube, there are no measurable differences in terms of frame geometry as compared with the "NuRoad" (kek), their dedicated gravel bike. No mounting points for racks, that's about it. Regarding the components, it came with 33mm cx tires, swapped them for 40mm gravel tires, no problemo. Cx crankset (46-36) is awesome by the way, due to the closer ratio than the compacts or sub-compacts you typically find on gravel rigs.
So, all things considered, if you find a good deal on a cx bike, you can often use it as a gravel bike without a problem. Just make sure you take a good look at the geo chart, tire clearance etc.
Pic related.