Sad to say, these issues persist even now with Xcode 12.5.1 and MacOS 11.4 It sure looks like a bug, because alternative APIs to achieve more-or-less the same, are still supported and seem to work. In my current code I use the combination of:     ProcessSerialNumber psn = { 0, kCurrentProcess };     TransformProcessType(&psn, kProcessTransformToForegroundApplication);     [[NSRunningApplication currentApplication] unhide]; [NSApp activateIgnoringOtherApps:YES]; As alternative to the always failing     if ( [NSApp setActivationPolicy: NSApplicationActivationPolicyRegular] == NO)         os_log_error(preventionUILog, "Failed to change ActivationPolicy to Regular"); Hope this helps somehow...

Mine is an Obj-C MacOS X project with several targets, Running latest Xcode 12.5.1. Failing target is a normal Cocoa App. It started failing with this exact error after I dragged an image file to the project (into Resources group/directory), added to the target and tried to build. I use this image resource programmatically. Failed again and again. Removing the image removed the problem. I found the image file WAS NOT copied to the project repo, and the reference pointed to somewhere outside the repo. I deleted the reference from the project, copied the actual file into the project repository, re-added it to my project/group and target. Verified the reference was now inside the project repo (relative to group, with just the file name as a 'path'). Now it built OK. I then dragged another image (this time I first copied it into my Resources group/directory) and sad to say - the problem resurfaced. Reading other answers here, I saw the proposed build script: xattr -cr ~/Library/Developer/Xcode/DerivedData || echo Clear So I started to suspect the actual image files had something about them that was not to Xcode's liking. so... a Quick Terminal shell: mini-mac7:Resources $ ls -la@    total 392 drwxr-xr-x   5 mshneor  staff     160 Jun 28 13:57 . drwxr-xr-x  12 mshneor  staff     384 Jun 28 13:44 .. -rw-r--r--@  1 mshneor  staff   19688 Jun 28 13:44 MyPtShield.png com.apple.lastuseddate#PS     16  -rw-r--r--@  1 mshneor  staff  172435 Mar 16  2017 My-logo-reg-K.png com.apple.FinderInfo     32  com.apple.lastuseddate#PS     16  com.apple.quarantine     57  -rw-r--r--@  1 mshneor  staff     258 Jun 28 13:44 factoryDefaults.plist com.apple.lastuseddate#PS     16  And sure enough - both image files DO HAVE extra information and extended attributes. So this time, I ran that script once, directly at my Resources directory, thus removing all Extended attributes from the resource files, like this mini-mac7:Resources $ xattr -cr . || echo Clear mini-mac7:Resources $ ls -la@                   total 392 drwxr-xr-x   5 mshneor  staff     160 Jun 28 13:57 . drwxr-xr-x  12 mshneor  staff     384 Jun 28 13:44 .. -rw-r--r--   1 mshneor  staff   19688 Jun 28 13:44 PfPtShield.png -rw-r--r--   1 mshneor  staff  172435 Mar 16  2017 Proofpoint-logo-reg-K.png -rw-r--r--   1 mshneor  staff     258 Jun 28 13:44 factoryDefaults.plist mini-mac7:Resources $  And sure enough - next build worked like a charm. I really hope git is smart enough to push the removal of extended attributes to the repo too.