Really? You’ve interested me enough to go source it.

For the amount of professional salaried employees, I found this: Over 18 million office workers were employed in the U.S. as of May 2020, earning an average salary of ​$42,390​ per year, or ​$20.38​ per hour, according to the U.S. Bureau of Labor Statistics (BLS)..

For the total amount of US workers, I found this: In 2019, around 157.54 million people were employed in the United States. For 2022, an increase by almost 2 million employed people is expected.

So around a 10% is actually strikingly accurate. I realize those aren’t the same data sources at the same exact time, but if I just do a naive division I get: 11.42% of American adults are employed as professional salaried employees.