What is your operating system?
MacOS Catalina 10.15.7
What is your Shotcut version (see Help > About Shotcut)? Is it 32-bit?
Can you repeat the problem? If so, what are the steps?
I had a convert to edit friendly format job running and I selected another video to do the same. I was typing in the file name when Shotcut crashed. I’m not entirely sure but I suspect this occurred when the first convert job had completed.
I have not been able to repeat (so far). However I got a core dump from the process and it shows a free of an unallocated pointer:
Process: Shotcut 
Version: 20.10 (20.10.31)
Code Type: X86-64 (Native)
Parent Process: ??? 
Responsible: Shotcut 
User ID: 501
Date/Time: 2020-11-21 17:16:45.730 +0000
OS Version: Mac OS X 10.15.7 (19H15)
Report Version: 12
Anonymous UUID: 649F68FA-94C1-F03C-DB64-0DEC5FE49FD8
Sleep/Wake UUID: 28C278EF-A170-42E8-8904-64FA19BB32FE
Time Awake Since Boot: 41000 seconds
Time Since Wake: 2300 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:
Shotcut(28447,0x110de6dc0) malloc: *** error for object 0x7ffeef167760: pointer being freed was not allocated