Hmm, my iPhones work fine regarding connection but... honestly I have to tell you no source powered Dongle I tried so far (L&P W2 or Go Bar) sounded as good out of IPhones compared to USB-C sources.
I realize it each time I connect Go Bar to my IPad Air M1 or Android Phone that the presentation is more dynamic and detailed like a veil is lifted.
Iphone 13 Pro and 11 Pro sound more relaxed and somehow veiled.
Depending on the IEM / headphone, recording that more mellow presentation can be suitable for some people but I started avoiding lightning connections for that reason alone.
My explanation is the different USB specifications for lightning vs usb c where USB C might provide more juice for the Dongle.
Maybe that'll change as soon as new IPhone models will feature USB-C soon...
For battery powered DAPs it's a different story as any iPhone will provide a bit perfect connection for sound only and work like a charm without disadvantages (imho)