[James2001]

It's usually the same on shows that are wider than 16:9, they're still 16:9 on the master tape, with the letterboxing part of the picture. Will presumably be the same here- still a 16:9 master, just with black bars baked in. No different really to how music videos and adverts were done in 4:3 with faux-letterbox effects up until the 16:9 era.

Watching The Santa Clauses on Disney+, whenever there's a clip from the original film, the picture opens up from 2.35:1 to 16:9, which shows that the letterboxing is an effect rather than the show being mastered in 2.35:1.