I am on Xcode 12.4 and also having this problem with my Flutter project. Earlier today it was opening fine, then I quit Xcode, built a new ios version of the app through VS terminal, then tried to reopen my project in Xcode but nothing happens when I click on the .xcworkspace file, it doesn't open anything. It does open other projects successfully, but still not the one above. After restarting Mac and trying again, it still does not open, but gave me the message: Xcode quit unexpectedly Process: Xcode [2379] Path: /Applications/Xcode.app/Contents/MacOS/Xcode Identifier: com.apple.dt.Xcode Version: 12.4 (17801) Build Info: IDEFrameworks-17801000000000000~7 (12D4e) App Item ID: 497799835 App External ID: 839994694 Code Type: X86-64 (Native) Parent Process: ??? [1] Responsible: Xcode [2379] User ID: 501 Date/Time: 2021-04-02 18:33:36.412 +0100 OS Version: Mac OS X 10.15.7 (19H2) Report Version: 12 Bridge OS Version: 4.6 (17P6610) Anonymous UUID: 539C0A09-D3B8-3B12-BC86-25902B07D97B Time Awake Since Boot: 500 seconds System Integrity Protection: enabled Crashed Thread: 0 Dispatch queue: com.apple.main-thread Exception Type: EXC_CRASH (SIGABRT) Exception Codes: 0x0000000000000000, 0x0000000000000000 Exception Note: EXC_CORPSE_NOTIFY Application Specific Information: ProductBuildVersion: 12D4e ASSERTION FAILURE in /Library/Caches/com.apple.xbs/Sources/IDEFrameworks/IDEFrameworks-17801/IDEKit/Workspace/IDEWorkspaceDocument.m:3270 Details: (tabController) should not be nil. Object: IDEWorkspaceDocument: 0x7f8d74189ed0 Method: -commitStateToDictionary: Thread: NSThread: 0x7f8d6f81a630{number = 1, name = main} Open FDs: 38/7168 Hints: There are a lot more lines underneath but too long to post here. Any help on this will be appreciated, currently blocking new version going live.