He got more than his opponent the second time. Trump got 49.8%, Harris got 48.3%. This is widely considered to be winning the popular vote; nobody else got more votes than he did.
As opposed to 2016 where Trump won the electoral college but received fewer total votes than his major opponent because extra votes in California don't count in the electoral college.
Notice that if you want to claim that winning the popular vote requires more than 50% then you can't claim that Clinton "won the popular vote" in 2016 because she got 48.2% to Trump's 46.1%.
As opposed to 2016 where Trump won the electoral college but received fewer total votes than his major opponent because extra votes in California don't count in the electoral college.
Notice that if you want to claim that winning the popular vote requires more than 50% then you can't claim that Clinton "won the popular vote" in 2016 because she got 48.2% to Trump's 46.1%.