steep learning curve
The phrase for how hard a skill is to learn.
People use steep learning curve to mean that a skill is hard to learn at first. In the technical graph the phrase came from, a steep curve means rapid progress. If you mean the work is hard, use hard to learn. Do not lean on the phrase when the plain words will do.
Examples
Use The new software is hard to learn.
Avoid The new software has a steep learning curve.