My friend and photographer Domingo Milella sent me the link to a video interview of Jeff Wall. I am a big fan of him and I hope that you will find a moment to listen to what he says.

I transferred the mail to Valerio Spada, another friend and photographer:
I have already seen this video, but every time it drives me crazy.

Valerio answered me:
In fact, he uses a 4×5… thank you, I will download it if I can and I will check it tomorrow on the plane. I have already watched it I guess, but I will be happy to check it again.
Read that if you had not, 4×5 wins.
https://www.wsj.com/articles/jeff-walls-unique-photographic-vision-1441375796

I answered: Jeff has never used a 4×5, he has always used a 8×10.

Valerio:
Yeah… you can tell it from this 4×5 Linhof (of course the most expensive on the market, but still a 4×5)…

He might have used it for the smaller pictures but, since the very beginning, he uses a Linhof 8×10.

Email chain from June 25, 2018.