They used Deep Fake video and audio technology to allow seventy-year-old Mark Hamill (Luke Skywalker) to perform for about thirty minutes as a convincing 30-year-old Mark Hamill (Luke Skywalker).

Luke Skywalker was 28 years old for Return of the Jedi. Mark Hamill was about 31 during the filming of Return of the Jedi.

Deep Fakes and de-aging have been used in movies before. De-aging does not look as convincing.

Deep Fakes have been used around Youtube for short clips but this is using a high resolution for an hour-long TV show.

This shows that actors can be substituted for entire high-resolution movies. They can be made to look and sound convincingly younger or older. People can be substituted. Aliens who look more like any animal can be created.