I had the same issue with the 2020 version of TurboTax on a MacBook Pro running MacOs Big Sur 11.2.
Try to:
1 - Create a new user account on your Mac and run Turbotax from that account. If that works, there is some corruption with the old account that you used on the Mac.
2 - I resolved this by deleting all files under ~/Library/Caches/KSCrash/TurboTax
Subsequently I was able to startup TurboTax 2020 with no issues.
The log under ~/Library/logs/com.intuit.turbotax/2020/*log will show:
2021-02-02 22:09:29.314 TurboTax 2020[6918:240595] error creating directory: Error Domain=NSCocoaErrorDomain Code=513 "You don’t have permission to save the file “ZipFiles” in the folder “KSCrash”." UserInfo={NSFilePath=file:///Users/pvanamstv2/Library/Caches/KSCrash/ZipFiles, NSUnderlyingError=[phone number removed]90 {Error Domain=NSPOSIXErrorDomain Code=13 "Permission denied"}}
2021-02-02 22:09:29.330 TurboTax 2020[6918:240595] [Crashlytics] Version 3.9.3 (128)
2021-02-02 22:09:29.367 TurboTax 2020[6918:240595] EngineUpdate - setSparkleDefaults entered
2021-02-02 22:09:29.368 TurboTax 2020[6918:240595] EngineUpdate - startAnESDAppUpdateCheck - SKUName - premier, Product Year - 2020, Current Version - [phone number removed]
2021-02-02 22:09:29.483 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.512 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.518 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.533 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.541 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.544 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.548 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.551 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.554 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.556 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.558 TurboTax 2020[6918:240595] ESD:Validating xml Signature...
2021-02-02 22:09:29.562 TurboTax 2020[6918:240595] EngineUpdate - 10 packages info recieved from ESD
2021-02-02 22:09:29.562 TurboTax 2020[6918:240595] EngineUpdate - TTMac product is already up-to-date to version [phone number removed]
2021-02-02 22:09:29.691 TurboTax 2020[6918:240595] Terminate called after uncaught c++ exception:
0 TurboTax 2020 [phone number removed]a5f97b PrintStackAndTerminateOnUncaughtCPPException + 59
1 KSCrash [phone number removed]c99e10 _ZL21CPPExceptionTerminatev + 86
2 TurboTax 2020 [phone number removed]206319 _ZL19CLSTerminateHandlerv + 360
3 libc++abi.dylib 0x00007fff203f9847 _ZSt11__terminatePFvvE + 8
4 libc++abi.dylib 0x00007fff203f97e9 _ZSt9terminatev + 41
etc, etc.
Deleting the directory and will files under step 2 resolved this issue for me. I spent 4 hours on the phone with TurboTax support and they were of no help at all
