That’s false. You can apply for EB visas from outside the US. After the approval of the I-140 (application for employment-based visa), instead of “adjustment” of your visa status in the US, you perform immigrant visa processing at your local consulate to get your green card.
You can still travel after filing the I-140 but not after filing the I-485 (adjustment) without advance parole.
You can still travel after filing the I-140 but not after filing the I-485 (adjustment) without advance parole.