He did go after Hillary but his DOJ couldn't find a thing to prosecute her.
Donald Trump publicly advocated for prosecuting Hillary Clinton, especially during the 2016 presidential campaign, where chants of "Lock her up!” became a hallmark of his rallies. He often criticized Clinton for her use of a private email server during her time as Secretary of State and suggested she had committed crimes.
After becoming president, Trump continued to express frustration about Clinton's lack of prosecution. In November 2017, The New York Times reported that Trump had privately pressured then-Attorney General Jeff Sessions to look into appointing a special counsel to investigate Clinton. However, Sessions and other Justice Department officials did not pursue the matter, citing a lack of sufficient evidence and the potential damage to the department's independence.
In later statements, former officials, including those from the Justice Department, confirmed that while Trump frequently discussed prosecuting Clinton, his aides and legal advisers dissuaded him, worried that it would look like using the justice system for political purposes. Ultimately, no formal investigation into Clinton was launched during Trump's administration.