Turned it off after about 5 mins, just couldn't deal with 4:3, seems like I saved myself nearly 4 hours of misery
That because 2:33:1 (do you mean 2.39:1?) is the aspect ratio for Cinema, some would say the natural home of motion pictures, watching it at home where predominately it's 16:9 then you get black bars.
As other have already said it seems that Synder was really more worried abou IMAX than home viewing, not sure how the really lines up with the reality of all cinemas being shut, Directors huh!
https://www.denofgeek.com/movies/zack-snyder-justice-league-4-3-aspect-ratio/
Yeah there's a reason why nobody's doing that Zack, especially in a global pandemic

To be fair I guess this was in production long before the pandemic hit, some will admire his commitment to watching a film at the Cinema (IMAX) in order to get the best viewing experience.