Performing a manual on a road / gravel bike
You are correct. The geometry of a road bike leads to a different body weight distribution than you would have by default on an MTB, BMX or other type of a bicycle. To lift the front wheel, you'll need to shift your mass center to the left of the rear wheel's axle to ground projection, that's just statics in physics.
You can ease it slightly by e.g. installing a shorter stem and by lowering the saddle, but it still would not be enough to make it as easy as it would be on certain other bicycle types.
It is not impossible, you may find videos on the Internet of people doing manuals, front manuals and whatnot on road bicycles. By as for the beginner, it would take much more time and frustration to learn it on a road bike frame.