iOS app freezes on launch screen Unity 2019.4.12f1 on device

I am trying to update an iOS app. It just had a white splash screen and I used a scene to do an intro. I want to use a white splash screen still. I saw that in version 2019.4.12f1 that I could have Unity make the mandatory storyboards using iPhone and iPad Launch Screen options in the Player settings:

I did this and I do get my white screen (and it shows an image if I add one) - BUT it does not progress from there. it is just unresponsive. With no errors in Xcode. What should I check? - I am using a release version. Is there something I should check in Xcode?



Actually, I do have a warning:
clang: warning: argument unused during compilation: ‘-mno-thumb’ [-Wunused-command-line-argument]

And I see that someone else with this warning had a similar problem:

Why is this argument being generated?
Is this the likely cause of the bug?
What are the work-arounds?