The truth is that we cannot know or do what is good apart from Jesus Christ. It is not that people who don’t know Christ as their Lord and Savior actually do good, and that Christians must account for the good that they do apart from Christ.
No, that frames the problem in the wrong way. Rather, people who don’t know Christ as their Lord and Savior, but who actually do good, don’t themselves know that it is Christ’s prevenient grace in their own lives that allows them to do good. And it is they who must account for their own failure to recognize the truth of Jesus Christ in their own lives who is actually animating the good that they do.