Which design software are mostly used by mechanical engineers around the world?

"I want to know if I am practicing the trending design software or just wasting the time"

Depend very much on what you want to achieve. If you want just to put your imagination on a file, Fusion is OK. But if you want to build complex assemblies, then i recommend Inventor.

Inventor use solids as main element, with a huge Content Center (for example, here you can find fasteners, like bolts, nuts, so on, shaft parts like bearings, keys, ecc., tube and pipe parts like flanges, nipples, so on). By using solids, you have mass, torque, forces, gravity, ecc., so you can do advanced simulation and analyses.

Other CAD (3DSMax) programs use surfaces as a main element. Is more easy to model, cut, pull. And is more useful for 3D printing, as the STL files are using the outer surface to generate the internal fill.

So depend very much on what you to achieve.

No Problem.Grabcad community work with a lot of programs such as:
CATIA
SolidWorks
3DSMAX
NX
.
.
.
Of course, the statistical community of AutoCAD Fusion is much less,That can be reduce your learning speed.

But i suggest you that upload IGES/STP files to grabcad , so that many users can be view your files with their own software.

Good luck!