Got the same problem.
Path:									/Applications/Xcode.app/Contents/MacOS/Xcode
Identifier:						Xcode
Version:							 12.3 (17715)
Build Info:						IDEFrameworks-17715000000000000~8 (12C33)
Code Type:						 X86-64 (Native)
Parent Process:				??? [1]
Responsible:					 Xcode [667]
User ID:							 501
Date/Time:						 2020-12-22 19:20:55.163 +0800
OS Version:						Mac OS X 10.15.7 (19H114)
Report Version:				12
Anonymous UUID:				51CFAD95-2744-E6C9-F640-20B13531F49F
Time Awake Since Boot: 80 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: 12C33
ASSERTION FAILURE in /Library/Caches/com.apple.xbs/Sources/IDEFrameworks/IDEFrameworks-17715/IDEKit/Workspace/IDEWorkspaceDocument.m:3270
Details:	(tabController) should not be nil.
Object:	 <IDEWorkspaceDocument: 0x7ffcd2158910>
Method:	 -commitStateToDictionary:
Thread:	 <NSThread: 0x7ffcce905a00>{number = 1, name = main}
Open FDs: 42/9472
Hints:	
Backtrace:
	0	 -[IDEAssertionHandler handleFailureInMethod:object:fileName:lineNumber:assertionSignature:messageFormat:arguments:] (in IDEKit)
	1	 _DVTAssertionHandler (in DVTFoundation)
	2	 _DVTAssertionFailureHandler (in DVTFoundation)
	3	 -[IDEWorkspaceDocument commitStateToDictionary:] (in IDEKit)
	4	 -[DVTStateToken _copyStatefulObjectState] (in DVTFoundation)
	5	 -[DVTStateToken pushStateToRepositoryAndReturnError:] (in DVTFoundation)
	6	 -[DVTStateRepository _updateStateIfNeeded] (in DVTFoundation)
	7	 -[DVTStateRepository collectStateFromRegisteredObjects] (in DVTFoundation)
	8	 -[IDEWorkspaceDocument writeStateData] (in IDEKit)
	9	 __28-[IDEWorkspaceDocument init]_block_invoke (in IDEKit)
10	 -[DVTDelayedInvocation runBlock:] (in DVTFoundation)
11	 __NSFireDelayedPerform (in Foundation)
12	 CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION (in CoreFoundation)
13	 __CFRunLoopDoTimer (in CoreFoundation)
14	 __CFRunLoopDoTimers (in CoreFoundation)
15	 __CFRunLoopRun (in CoreFoundation)
16	 CFRunLoopRunSpecific (in CoreFoundation)
17	 RunCurrentEventLoopInMode (in HIToolbox)
18	 ReceiveNextEventCommon (in HIToolbox)
19	 _BlockUntilNextEventMatchingListInModeWithFilter (in HIToolbox)
20	 _DPSNextEvent (in AppKit)
21	 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] (in AppKit)
22	 -[DVTApplication nextEventMatchingMask:untilDate:inMode:dequeue:] (in DVTKit)
23	 -[NSApplication run] (in AppKit)
24	 NSApplicationMain (in AppKit)
25	 start (in libdyld.dylib)
abort() called
Application Specific Signatures:
((tabController)) != nil
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0	 libsystem_kernel.dylib				 0x00007fff7355b33a __pthread_kill + 10
1	 libsystem_pthread.dylib			 0x00007fff73617e60 pthread_kill + 430
2	 libsystem_c.dylib						 0x00007fff734e2808 abort + 120
3	 com.apple.dt.IDEKit					 0x000000010ba3f9e2 +[IDEAssertionHandler _handleAssertionWithLogString:assertionSignature:assertionReason:extraBacktrace:] + 1275
4	 com.apple.dt.IDEKit					 0x000000010ba3fee8 -[IDEAssertionHandler handleFailureInMethod:object:fileName:lineNumber:assertionSignature:messageFormat:arguments:] + 1068
5	 com.apple.dt.DVTFoundation		 0x00000001090d428b _DVTAssertionHandler + 476
6	 com.apple.dt.DVTFoundation		 0x00000001090d448e _DVTAssertionFailureHandler + 306
7	 com.apple.dt.IDEKit					 0x000000010b95aeca -[IDEWorkspaceDocument commitStateToDictionary:] + 2146
8	 com.apple.dt.DVTFoundation		 0x0000000108f728a1 -[DVTStateToken _copyStatefulObjectState] + 143
9	 com.apple.dt.DVTFoundation		 0x0000000108f72aba -[DVTStateToken pushStateToRepositoryAndReturnError:] + 77
10	com.apple.dt.DVTFoundation		 0x000000010900e2d7 -[DVTStateRepository _updateStateIfNeeded] + 352
11	com.apple.dt.DVTFoundation		 0x000000010900f2a6 -[DVTStateRepository collectStateFromRegisteredObjects] + 79
12	com.apple.dt.IDEKit					 0x000000010b95864a -[IDEWorkspaceDocument writeStateData] + 511
13	com.apple.dt.IDEKit					 0x000000010b944939 __28-[IDEWorkspaceDocument init]_block_invoke + 180
14	com.apple.dt.DVTFoundation		 0x0000000108e96e05 -[DVTDelayedInvocation runBlock:] + 860
15	com.apple.Foundation					 0x00007fff3ba386f2 __NSFireDelayedPerform + 415
16	com.apple.CoreFoundation			 0x00007fff3937e7f9 CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION + 20
17	com.apple.CoreFoundation			 0x00007fff3937e35f __CFRunLoopDoTimer + 859
18	com.apple.CoreFoundation			 0x00007fff3937de47 __CFRunLoopDoTimers + 322
19	com.apple.CoreFoundation			 0x00007fff39362bea __CFRunLoopRun + 1871
20	com.apple.CoreFoundation			 0x00007fff39361e3e CFRunLoopRunSpecific + 462
21	com.apple.HIToolbox					 0x00007fff37f8eabd RunCurrentEventLoopInMode + 292
22	com.apple.HIToolbox					 0x00007fff37f8e7d5 ReceiveNextEventCommon + 584
23	com.apple.HIToolbox					 0x00007fff37f8e579 _BlockUntilNextEventMatchingListInModeWithFilter + 64
24	com.apple.AppKit							 0x00007fff365d4039 _DPSNextEvent + 883
25	com.apple.AppKit							 0x00007fff365d2880 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 1352
26	com.apple.dt.DVTKit					 0x000000010979cd07 -[DVTApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 421
27	com.apple.AppKit							 0x00007fff365c458e -[NSApplication run] + 658
28	com.apple.AppKit							 0x00007fff36596396 NSApplicationMain + 777
29	libdyld.dylib								 0x00007fff73413cc9 start + 1
luiswu
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Hi! There,
I am a colleague of darkes. the Feedback ID is FB7751440. Thank you!
Luis.