Having the same issue. I use Unity 2020.3.18f1 and stack trace looks like
#0 (null) in __psynch_cvwait ()
#1 (null) in _pthread_cond_wait ()
#2 0x0000000109abd7cc in il2cpp::os::posix::PosixWaitObject::Wait(unsigned int, bool) ()
#3 0x0000000109ab5190 in il2cpp::os::Thread::Join() ()
#4 0x0000000109adb028 in il2cpp::vm::Thread::KillAllBackgroundThreadsAndWaitForForegroundThreads() ()
#5 0x0000000109ae81a8 in il2cpp::vm::Runtime::Shutdown() ()
#6 0x000000010939ab60 in CleanupIl2Cpp() ()
#7 0x00000001092b1740 in PlayerCleanup(bool) ()
#8 0x000000010967ce74 in UnityCleanup ()
#9 0x0000000108db2a20 in -[UnityAppController applicationWillTerminate:] at /..../build/ios/Classes/UnityAppController.mm:490
#10 (null) in -[UIApplication _terminateWithStatus:] ()
Although it doesn't affect user experience, I see many crashes on appstore connect page which leads to worse ASO so I need help if anyone has better understanding.