Why has the Xcode team not solved this problem. It's been a consistent complaint since the interface builder was released. Xcode has git support out of the box. I have to think a visual differ would've been along by now.
Complaints happen; it doesn't mean the complainers are using the tool correctly.
But it does raise a possibility: Maybe the Xcode team could make it easier for a developer to do something along the lines of checking out a single scene to work on, at least putting other developers on notice that they will be risking merge issues if they work on the same scene.
Normally issues can be avoided by just coordinating work such that people aren't editing the same code at the same time. This goes for XIB or storyboard "code" too. Yes maybe Xcode could do something, but that something would probably address developer behavior more than it would address merging per se.
That doesn't address the fact that properly reviewing changes made by others to xib files generated by Xcode pretty much requires you to check out those changes and review them in interface builder. That's a lot of friction for larger teams who don't just do iOS development.
As I said in my article I don't think interface builder is terrible or anything, I just think it's a poor fit for larger teams doing cross functional development.
There is a reason why you hear this constant complaint, and the reason is because IB is really horrible in this regard. Behind the scenes it is generating unnecessarily verbose xml that is not developer friendly at all. This is unacceptable. Even Microsoft did a much better job when generating XAML from Expression Blend, and this was half a decade ago.
I'm not sure if you've ever used react-native, but imagine if IB generated ode that looked like a react component. Not a single soul would be complaining because these problems wouldn't exist.