Stage, screen, voice-overs–you name it and Mark Hamill has done it. And yet, for the return of Luke Skywalker in The Book of Boba FettHamill says the team used a completely new form of acting: a composite performance.
The documentary gives the Luke Skywalker transformation probably more time than anything else, and it’s better to see it than me to describe it. Basically, though Hamill acted the performance, actor Graham Hamilton also acted the performance (with direction from both Filoni and Hamill), and all were filmed with a special camera rig that captured it with multiple angles. Then, digital effects were blended with deep fake techniques to create the final image.
Again, this section is excellent and you should check it out. It runs for about six minutes beginning around the 44-minute mark.