in this thread many people have clearly never developed for iOS

Here's just the screen sizes, not even taking into account actual resolution:

    iPhone (2007)     3.5" 74.0 × 49.3    36 cm²
    iPhone 5          4.0" 88.6 × 49.8    44 cm²
    iPhone 12 mini    5.4" 124.5 × 57.5   72 cm²
    iPhone Duo, cover 5.4" 113.4 × 77.2   88 cm²
    iPhone 6 Plus     5.5" 121.8 × 68.5   83 cm²
    iPhone X          5.8" 133.7 × 61.8   83 cm²
    iPhone Air        6.5" 150.0 × 69.1  104 cm²
    iPhone 18 Pro Max 6.9" 159.2 × 73.3  117 cm²
    iPhone Duo, inner 7.6" 157.6 × 111.5 176 cm²

Good list. And if you support both portrait and landscape, you need to support twice that, and you need to be able to switch on the fly.

But for the apps that don't currently support both orientations, it's possible they don't have support for switching aspect ratio on the fly. This design might help with those apps not completely breaking when folding/unfolding.