Reinstalling Big Sure appears to have fixed the problem.
So the error I am getting from IBDesignables is:
dlopen(app name.app, 1): no suitable image found. Did find:
AppName.app: macho-0, but wrong architecture
I had excluded ARM64 in order to get Xcode to build to Simulator when I first got my M1 MacBook Air. So I removed the exclusions and built again and Xcode suddenly seems more stable, running for longer without the spinner. This is even though IBDesignable error still exists (after clean/deleting derived data) and I still get the spinner if I click on the error message in Storyboards.
None of my fixes are working, forced to just restart Xcode every 1-5 minutes when beachball appears.
In my case it's possible I have an IBDesignable issue, it's a large project with some IBDesignable errors in storyboards (that I didn't make). I'm curious why it always takes a few minutes to beach ball, seems like a background process that might be doing something to storyboards and takes that long to start.
You can also try
xcrun simctl shutdown all && xcrun simctl erase all
to entirely reset simulator. That helped me the first two times.
Edit: And so far looks to have fixed the third time too.
I had this happen twice two weeks ago, and was able to get the problem to go away by
deleting xcuserdata: folder from both of your .xcodeproj & .xcworkspace
defaults delete com.apple.dt.Xcode
rm -r ~/Library/Developer/XCode/DerivedData
rm -r /Applications/Xcode.app
rm -r ~/Library/Caches/com.apple.dt.Xcode
rm -r ~/Library/Developer
rm -r ~/Library/MobileDevice
rm ~/Library/Preferences/com.apple.dt.Xcode.plist
restart mac
But unfortunately it's happening again, and these process isn't fixing it. In my case it appears to happen with any project.
Post not yet marked as solved
And it's happening again. This is what I'm doing to fix it.
rm ~/Library/"Saved Application State"/com.apple.dt.Xcode.savedState/*
defaults delete com.apple.dt.Xcode
rm -rf ~/Library/Developer
Right click yourprojectname.xcodeproj
Show package contents.
Delete xcuserdata.
Right click on project.xcworkspace
Show package contents
delete the xcurserdata.
For some reason still had to run
xcrun simctl shutdown all && xcrun simctl erase all
I had same problem with my GM release, named "Xcode 12". I guess Xcode's developers made some incorrect assumptions about it's file name.
Post not yet marked as solved
Of course, run destination was the key point. I was debugging on a 5s, which apparently isn't 64 bit. Switching to an iPhone 8 simulator fixes the problem. my bad.
Post not yet marked as solved
On an actual device with XCode 11.4.1 I'm having same problem "No reply dictionary received from LeakAgent request." But I can get the memory node graphs to work when running in 13.4 simulator.
