I also ask what they did to recreate a young Sarah Connor at the beginning of the same movie trying and failing to protect John. Only makeup?
How ‘Dark Fate’ Visual Effects Team Brought ‘Terminator’ Stars Back to the ’90s
For the flashback sequence in Dark Fate, the team did digital head replacement on younger actors who functioned as body doubles and were filmed on set. The digital work started with a scan of each original actor. Then the team used a markerless facial capture system called Anyma, developed by Disney Research, to capture each actor’s performance.
That scene actually looks very real.
Here is a video on how they made it
Looks like they got younger body doubles to do the scenes, mapped the facial features of the relevant actors using a digital tool called Anyma, and had them act the scenes the body doubles had done, then de-aged the faces and mapped the de-aged faces to the body doubles.