I'm facing the same issue too.
It was working fine till Xcode 12 beta 2 but since beta 3 it is crashing. Tried many things but not able to get to a conclusion.
Path:									/Users/USER/Downloads/Xcode.app/Contents/MacOS/Xcode
Identifier:						com.apple.dt.Xcode
Version:							 12.0 (17219)
Build Info:						IDEFrameworks-17219000000000000~2 (12A7209)
Code Type:						 X86-64 (Native)
Parent Process:				??? [1]
Responsible:					 Xcode [2742]
User ID:							 882789207
Date/Time:						 2020-09-28 16:24:52.905 -0400
OS Version:						Mac OS X 10.15.4 (19E287)
Report Version:				12
Bridge OS Version:		 3.0 (14Y908)
Anonymous UUID:				42335963-5875-5860-05E1-3D2F68B041CF
Time Awake Since Boot: 780 seconds
System Integrity Protection: enabled
Crashed Thread:				19	Dispatch queue: XCBuild.XCBBuildOperation.buildOperationHandlerQueue
Exception Type:				EXC_BAD_INSTRUCTION (SIGILL)
Exception Codes:			 0x0000000000000001, 0x0000000000000000
Exception Note:				EXC_CORPSE_NOTIFY
Termination Signal:		Illegal instruction: 4
Termination Reason:		Namespace SIGNAL, Code 0x4
Terminating Process:	 exc handler [2742]
Application Specific Information:
ProductBuildVersion: 12A7209
Thread 0:: Dispatch queue: com.apple.main-thread
0	 com.apple.CoreFoundation			 0x00007fff348ee871 _CFRelease + 502
1	 com.apple.CoreFoundation			 0x00007fff348619ee CFRunLoopTimerSetNextFireDate + 472
2	 com.apple.CoreFoundation			 0x00007fff348224f5 CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION + 23
3	 com.apple.CoreFoundation			 0x00007fff34822427 __CFRunLoopDoObservers + 457
Siddhesh12
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After 2 weeks of research we were able to solve this.
We had objective c code in our code base - NSUserActivity+MediaPlayerAdditions.h
commenting out all the code from that file solved the issue.
NS_ASSUME_NONNULL_BEGIN
@interface NSUserActivity (MediaPlayerAdditions)
/// A unique identifier relative to the app's media content catalog for the displayed media item.
@property (nonatomic, copy, nullable) NSString *externalMediaContentIdentifier NS_AVAILABLE_IOS(10_1) TVOS_AVAILABLE(10_0_1) WATCHOS_UNAVAILABLE;
@end
NS_ASSUME_NONNULL_END
Hope this will help something solving this.