I know there are guys here who are very good at interpreting Apple's English. Per Apple statement in AppStore connect:
As a reminder, starting March 27, 2019 all new apps and app updates for iPhone or iPad, including universal apps, will need to be built with the iOS 12.1 SDK and support iPhone XS Max or the 12.9-inch iPad Pro (3rd generation). Screenshots for these devices will also be required.
As of now, March 31st, 2019 I still see iPhone XS Max and iPad 3rd generation 12.9 screenshot as "Optional" in the AppStore connect.
My apps are all built with iOS 12.1 and 12.2 now and I've been supporting X screens since long ago.
My internal problem is that I don't like how XS Max screenshots are presented in the AppStore app. They are so small that users can hardly see anything. Screenshots for older screen sizes are more visible and I think that might be a reason for a lot of fellow devs not providing XS Max screenshots at all. Probably for games with having one landscape screenshot shown they are ok, but for the data intensive apps they are a disadvantage, imho.
Is this "Optional" in XS Max and iPad 3rd gen 12.9 screenshots that is still in the AppStore Connect - is it a sign that some one at Apple just misinterpreted the submission requirement? I don't think screenshots were present in the original requirement from September 2018:
Starting March 2019, all new apps and app updates for iPhone, including universal apps, will need to be built with the iOS 12 SDK and support iPhone XS Max. All new apps and app updates for Apple Watch will need to be built with the watchOS 5 SDK and supportApple Watch Series 4.
Hope that someone can provide more insight or just thoughts on this.