"Mental jobs" as a complete expression has never crossed my research; however, I found that they usually use other terms when referring to careers that involve a lot of thinking, analyzing, problem-solving, creativity, and other complex mental processing. Terms as:
Mentally demanding jobs, Mentally challenging jobs, and Mentally complex jobs
In this article, they stated:
People with mentally demanding jobs such as surgeons, lawyers, civil engineers, and graphic designers may have better memory in old age, the study indicated.
In another article, they used the term "Mentally challenging jobs":
People with mentally challenging jobs, like air traffic controllers,
doctors and financial analysts, tend to stay mentally sharper while on
the job and following retirement, results of a new study suggest.
And they named their article:
Mentally demanding jobs linked to slower cognitive decline
You will find "Mentally complex jobs" in the previous articles, but it is used as a more general term such that it describes jobs where complexity with both people and data is involved.