Here is the crash log. I really had no clue what I got wrong:
2019-11-15 10:24:27.594873+0800 Playground[7385:707933] *** Assertion failure in -[UINavigationController popToViewController:transition:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKitCore_Sim/UIKit-3900.12.15/UINavigationController.m:8129
2019-11-15 10:24:27.647984+0800 Playground[7385:707933] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Tried to pop to a view controller that doesn't exist.'
*** First throw call stack:
(
0 CoreFoundation 0x00007fff23c4f02e __exceptionPreprocess + 350
1 libobjc.A.dylib 0x00007fff50b97b20 objc_exception_throw + 48
2 CoreFoundation 0x00007fff23c4eda8 +[NSException raise:format:arguments:] + 88
3 Foundation 0x00007fff256c9b61 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 191
4 UIKitCore 0x00007fff4713d9d1 __57-[UINavigationController popToViewController:transition:]_block_invoke + 620
5 UIKitCore 0x00007fff4713d67e -[UINavigationController popToViewController:transition:] + 753
6 SwiftUI 0x00007fff2c1107bd $s7SwiftUI21UIKitNavigationBridgeC3pop33_F345616596EA75D1F4200D7666E5E588LL8animatedySb_tF + 413
7 SwiftUI 0x00007fff2c10fa83 $s7SwiftUI21UIKitNavigationBridgeC20preferencesDidChangeyyAA14PreferenceListVF + 1267
8 SwiftUI 0x00007fff2c09b8fd $s7SwiftUI14_UIHostingViewC20preferencesDidChangeyyF + 477
9 SwiftUI 0x00007fff2c19a5bd $s7SwiftUI9ViewGraphC13updateOutputs2atyAA4TimeV_tF + 221
10 SwiftUI 0x00007fff2c4ed609 $s7SwiftUI16ViewRendererHostPAAE6render8interval17updateDisplayListySd_SbtFyyXEfU_yyXEfU_ + 1001
11 SwiftUI 0x00007fff2c4ed01a $s7SwiftUI16ViewRendererHostPAAE6render8interval17updateDisplayListySd_SbtFyyXEfU_ + 634
12 SwiftUI 0x00007fff2c4e1074 $s7SwiftUI16ViewRendererHostPAAE6render8interval17updateDisplayListySd_SbtF + 436
13 SwiftUI 0x00007fff2c67ce22 $s7SwiftUI14_UIHostingViewC14layoutSubviewsyyF + 226
14 SwiftUI 0x00007fff2c67ce45 $s7SwiftUI14_UIHostingViewC14layoutSubviewsyyFTo + 21
15 UIKitCore 0x00007fff47d34cfd -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 2478
16 QuartzCore 0x00007fff2b138d41 -[CALayer layoutSublayers] + 255
17 QuartzCore 0x00007fff2b13ef33 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 517
18 QuartzCore 0x00007fff2b14a86a _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 80
19 QuartzCore 0x00007fff2b0917c8 _ZN2CA7Context18commit_transactionEPNS_11TransactionEd + 324
20 QuartzCore 0x00007fff2b0c6ad1 _ZN2CA11Transaction6commitEv + 643
21 QuartzCore 0x00007fff2b0c743a _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 76
22 CoreFoundation 0x00007fff23bb1617 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
23 CoreFoundation 0x00007fff23bac0ae __CFRunLoopDoObservers + 430
24 CoreFoundation 0x00007fff23bac72a __CFRunLoopRun + 1514
25 CoreFoundation 0x00007fff23****16 CFRunLoopRunSpecific + 438
26 GraphicsServices 0x00007fff38438bb0 GSEventRunModal + 65
27 UIKitCore 0x00007fff4784fb68 UIApplicationMain + 1621
28 Playground 0x0000000109af3b9b main + 75
29 libdyld.dylib 0x00007fff51a1dc25 start + 1
30 ??? 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)