I hadn’t heard of Disney’s Gallery: The Mandalorian, but evidently it revealed more details about the Luke Skywalker scene. In response, according to Screen Rant,
VFX team Corridor Crew took the time to share their thoughts on the show’s process. From what they determined, Hamill was merely on set to provide some reference points for the creative team and the stand-in actor, Max Lloyd-Jones. The Mandalorian used deepfake technology to pull together Hamill’s likeness, and they combed through countless hours of Star Wars footage to find the best expressions.
I found the 6-minute segment pretty entertaining & enlightening. Check it out: