WWDC 2019 - iOS13 April 2020 requirement

so we need to up the deployment target in Xcode to any lower version eg say iOS 11?

No. The features described as being required all exist in iOS 11. What's required is that you adopt them.

The three bullet points are:

• Adopt Launch Storyboards
• Support any size
• Support Split Screen Multitasking

Let's talk about what these mean.

• At present, you can often get by with launch images instead of using a launch storyboard. If a launch image for a certain phone size is missing, that phone pretends this is a different (smaller) phone and zoom the display. That will cease to be legal; launch images will be dead.

• At present, the use of launch images allows an app to appear letterboxed or zoomed on a device for which it is not targeted; the device pretends, in effect, to be a lesser device with a smaller screen. That option will go away together with launch images.

• At present, an iPad app can opt out of fullscreen multitasking if you check Requires Full Screen in App Target in the target's General pane. The video seems to imply that this will no longer be possible (but then in the same sentence it says that it will be possible if your iPad app requires an "immersive experience").

That's all. None of the stuff you mentioned in your question is involved or implied. The presentation in the video is horribly unclear, however, and the exact meaning of these coming restrictions is yet to emerge.

[One thing that confuses me is the fate of compatibility mode on the iPad. Will iPhone-only apps still be permitted to exist? They are letterboxed on iPad, and they do not support fullscreen multitasking. Will all apps have to be iPad-only or Universal going forward? It isn't clear from the video.]

Split screen multitasking refers to the ability to have two apps open side-by-side on the iPad -- see Session 205 from WWDC2015 that talks about this. The requirement says that apps submitted after April 2020 must be able to run in this mode, that is, they must be able to work in layouts different than the standard fullscreen.

The two videos you linked are about multiple windows -- this is when your app can run multiple instances of itself side-by-side. This feature is not part of the new requirements.

One more thing. As I understand, it will be checked by moderators during submission to the App Store. I am not sure, but if we use enterprise codesign it will be possible to skip this restriction.