This has probably been true forever. I considered applying for an internship at a medical center back in the 80's. My adviser laughed and told me it was a slot created by an Indian professor and was intended to be filled by an Indian student.
In 1979, 14% of PhDs went to non-citizens. In 2024, it's 38%.
(Table 1-6 in https://ncses.nsf.gov/surveys/earned-doctorates/2024#data )