That was the allegation he made in his appeal in 2016. In 2019, he said he was planning on investigating him, not that he actually did..
Biden persuaded Ukraine to fire its prosecutor while he was investigating a natural gas firm that employed Biden’s son on its board.
thehill.com
Shokin told me in written answers to questions that, before he was fired as general prosecutor, he had made “specific plans” for the investigation that “included interrogations and other crime-investigation procedures into all members of the executive board, including Hunter Biden.”
Planning to investigate is not investigating.