Important correction: This problem only happens on macOS Ventura (latest beta). There's no issue on macOS 12.6.

@coderkid: i wonder if you have the same issue with Xcode 13.2 as it fixed this for me. although i never had this issue before Xcode 13.

I received a reply from Apple where they ask to check the forthcoming new update Xcode 13.2 RC: https://developer.apple.com/download/ I've been using it for two days and so far it looks like the issue is fixed there.

yes, same issue here. it's a huge bug in Xcode 13. there was no issue in beta 1. the problem started from beta 4. i thought it was fixed in the final release as it worked normally for a few hours. but now the same problem came back I'm re-submitting this bug to Apple. in the meantime, I'm back to working in Xcode 13 Beta 1 as there's no issue there.

Absolutely. While Apple did introduce some nice UI refinements on Big Sur, there are also several UI changes that are quite horrible and defy any common sense and basic rules of intuitive human-oriented UI design. Unfortunately, Apple didn't improve anything on Monterey. I'll soon submit several messages dedicated to each of the unfortunate UI changes on Big Sur.

That's great!! Thanks for putting it together. I thought of creating my own replacement, but your project seems to do exactly what I need (as well as any other Mac developer, in my view). The redesigned NSAlert on Big Sur is a total disaster. In addition to cutting off long messages, the center-aligned text is simply not suitable for human consumption. The entire centered alignment of elements is also tasteless and visually unappealing. Those who designed the alerts lack the very basic knowledge of text legibility as well as human-oriented UI design in general. It's a big embarrassment for Apple. They're supposed to have the best UI designers in the world. And yet it looks like Apple just grabs random people from the street to design certain UI elements. Sadly, despite overwhelmingly negative feedback from both users and developers, nothing was changed on Monterey. I hope to implement NSCustomAlert in all my apps as soon as possible. And hope that other developers will follow the suit. P.S. In your current code, the alert cannot be moved with the mouse. I solved this issue by removing the NSWindowStyleMaskDocModalWindow mask AND adding _panel.movableByWindowBackground = YES. I'll post this feedback on git as well.

I finally started implementing dark mode in my Mac apps. Since I myself am one of those who can't stand the dark mode, I didn't have any personal incentives to implement it. I do hear that many users like dark mode. And my apps are used by thousands of people. However, ever since dark mode was implemented on Mojave I received exactly 1 (one) request to implement it. So naturally it was never a high priority. I do believe that apps should support dark mode. Just wanted to share the actual feedback I received from users.

Ok I can confirm that this issue is FIXED in Xcode 12 beta 3. From Xcode release notes: •Fixed performance issues with NSTabView and hidden views in a storyboard or .xib canvas. (63008369, 64314634) Thank you Apple! Big relief.

This is just an update that nothing has changed in Xcode 12: After the announcement of Xcode 12, Apple finally contacted me regarding this bug and asked to check if it's fixed in Xcode 12. After trying Xcode 12 beta I can confirm that nothing has changed there. The bug remains exactly the same exhibiting exactly the same behavior.

Hi Tim,As Claude mentioned, I found what causes the problem (at least in my case) - you can see a detailed description in my post above from May 11.I updated my bug report to Apple with the new info - but I believe that's all we can do in this case. Until Apple fixes the problem, Xcode 11 won't work for us. Unless you already did, I encourage you to submit a bug to Apple too. Hopefully they'll take it seriously if hear from multiple users.You can still use Xcode 10 as you may know anyway.Thanks,Leo

Ok it looks like I could isolate this issue to a very specific case: a window with NSTabView.
Here's what I discovered:-If a project does not have a window with a tab view, the problem doesn't happen.
-If any of my projects has a window with tab view, the problem is always triggered once I touch this window or any of its elements in IB.
-If I don't bring this window into view and don't touch it - the problem doesn't happen. Other elements don't trigger it.
-If I delete the tab view, the problem goes away.-Bring back a tab view - problem comes back. It doesn't have to be the original tab view - even a new tab view from the Library will trigger the problem again.
-No other UI element affects the issue. Only tab view.-This only happens originally with my own projects (which all originated back in Xcode 2-4). I tried some other devs projects with window+tab view and there was no problem.-But I can reproduce the issue with projects that I didn't create - and even with brand new projects in Xcode 11 - if I copy a tab view from my project to a window in the new project.
-It's sufficient to have just a single window with a tab view and nothing else - so it's not the complicity of the xib that causes the issue.
 
 As you can see I'm having fun here. Very productive.
 I may soon share a brand new Xcode project with a xib that triggers the issue (here at least).Thanks,Leo

Does it occur with a new project as well ?It doesn't. But now I can trigger it even in new projects by bringing certain elements from my xibs. I'll post details soon.Are all elements, tools, … installed in the proper place ?Xcode installed everything it should.I don't see anything suspicious in the logs or Activity Monitor, and the issue happens without Xcode 10 present as well..Regardless, it looks like I could isolate it to a specific case finally - I'll post details soon.

I agree that there's nothing good about dealing with a rare bug in Xcode. This one is certainly rare - but I already heard from a developer on another forum who had exactly the same issue.It looks like it affects some projects that originated in earlier Xcode versions years ago.Regardless, it looks like by now I managed to isolate the issue to a very specific case in xib files.I'll post details soon. Hopefully, I now have much more specific and helpful info for Apple to deal with.

I understand your point.However, like I mentioned, the same problem happens on two different machines, including clean new accounts.I don't use any third-party package managers.Like I mentioned, Xcode 10 works normally under same conditions. As well as everything else.I also did invest hours of efforts doing all reasonable troubleshooting steps by now.There is a bug in Xcode 11 - because otherwise this problem wouldn't happen. And if Xcode does have a problem with installation or something else, it should clearly inform about it - instead of quitely disintegrating into a rotten mess. It's a bug either way.I do hope Apple will get back to me and work further on addressing the issue. They're usually fairly responsive when it comes to developer tools issues.Leo

I meant on any of my machines of course.I can assure you there's nothing wrong with my machines or my installation. I'm using Xcode since version 2 and never saw anything like this.Xcode 10 and all other apps are working fine on the same machines.There's evidently a severe bug in Xcode 11, which doesn't affect all users.I do hope we'll get to the bottom of it eventuallty.