The Red Sox are now over .500 but still in last place.
Since MLB expanded from 4 to divisions to 6 divisions, no team has ever finished over .500 and in last place. But the 2005 Nationals came close, finishing 81-81 and in last.
After that the best record by a last place team is 78-84. It's been done 3 times, twice by, you guessed it, the Red Sox, in 2015 and 2022.