I tried to open https://developer.mozilla.org/en-US/docs/Web/HTML/Element/optgroup this link on any iPhone device except 16.0. It is showing properly.
That means for this code below:
<label for="dino-select">Choose a dinosaur:</label>
<select id="dino-select">
<optgroup label="Theropods">
<option>Tyrannosaurus</option>
<option>Velociraptor</option>
<option>Deinonychus</option>
</optgroup>
<optgroup label="Sauropods">
<option>Diplodocus</option>
<option>Saltasaurus</option>
<option>Apatosaurus</option>
</optgroup>
</select>
the output optgroup shows options properly.
But when trying in iOS 16.0 (iPhone 13 pro max), then it is showing as this:-
https://i.stack.imgur.com/MHw35.png
That mean, for label text, it is showing two times. label="Theropods" and label="Sauropods" is shown two times.
Don't know how to solve it! Seems like iOS 16 bug, Any Idea?

I noticed this as well, it does appear to be an iOS/Safari bug