I've already done several iOS exports as part of my general testing and development work, and they all opened fine. To double check, I just did another iOS export and opened it in Xcode 12.0.1, and it opened and ran on an iPad just fine. So it seems to be working fine here. I'm sure Construct is exporting valid Xcode projects and so the problem is not with Construct.
Anyway, as I mentioned, we can't fix problems in Xcode - that's up to Apple, so if you have trouble, you'll have to contact their support.