Update: Ok, the original problem was missing entitlements. Now it fails with:
default Finder +[NSExtensionContext _allowedItemPayloadClasses] not implemented. Setting the allowed payload classes to <private>
default macmount-actions +[NSExtensionContext _allowedItemPayloadClasses] not implemented. Setting the allowed payload classes to <private>
error cfprefsd Couldn't open parent path due to [2: No such file or directory]
default macmount-actions NSApp cache appearance:
-NSRequiresAquaSystemAppearance: 0
-appearance: (null)
-effectiveAppearance: <NSCompositeAppearance: 0x14760ce80
(
"<NSAquaAppearance: 0x150811e30>",
"<NSSystemAppearance: 0x15080cc90>"
)>
default distnoted register name: com.apple.nsquiet_safe_quit_give_reason object: com.mycompany.macmount-actions token: 3b0000003b pid: 52332
default macmount-actions *** Assertion failure in -[FPUIActionExtensionContainerViewController _configureWithDomainIdentifier:], FPUIActionExtensionContainerViewController.m:129
error Finder Action with identifier (<private>) did finish with error (Error Domain=com.apple.ViewBridge Code=14 UserInfo={com.apple.ViewBridge.error.hint=<private>, com.apple.ViewBridge.error.description=NSViewBridgeErrorServiceBootstrap}).
error Finder FP Custom action sheet finished with error Error Domain=com.apple.ViewBridge Code=14 "(null)" UserInfo={com.apple.ViewBridge.error.hint=-[NSViewServiceMarshal bootstrap:withReply:] caught NSInternalInconsistencyException 'attempting to send message to non-existent action extension view controller' with backtrace (
"0 CoreFoundation __exceptionPreprocess + 176",
"1 libobjc.A.dylib objc_exception_throw + 60",
"2 Foundation -[NSCalendarDate initWithCoder:] + 0",
"3 FileProviderUI -[FPUIActionExtensionContainerViewController _configureWithDomainIdentifier:] + 164",
"4 FileProviderUI -[FPUIActionExtensionContainerViewController awakeFromRemoteView] + 692",
"5 ViewBridge -[NSViewServiceMarshal _bootstrap:replyData:completion:] + 1828",
"6 ViewBridge -[NSViewServiceMarshal bootstrap:withReply:] + 272",
"7 CoreFoundation __invoking___ + 148",
"8 CoreFoundation -[NSInvocation invoke] + 428",
"9 CoreFoundation -[NSInvocation invokeWithTarget:] + 64",
"10 ViewBridge -[NSVB_ViewServiceImplicitAnimationDecodingProxy forwardInvocation:] + 192",
"11 CoreFoundation ___forwarding___ + 976",
"12 CoreFoundation _CF_forwarding_prep_0 + 96",
"13 CoreFoundation __invoking___ + 148",
"14 CoreFoundation -[NSInvocation invoke] + 428",
"15 CoreFoundation -[NSInvocation invokeWithTarget:] + 64",
"16 ViewBridge -[NSVB_QueueingProxy forwardInvocation:] + 300",
"17 CoreFoundation ___forwarding___ + 976",
"18 CoreFoundation _CF_forwarding_prep_0 + 96",
"19 CoreFoundation __invoking___ + 148",
"20 CoreFoundation -[NSInvocation invoke] + 428",
"21 CoreFoundation -[NSInvocation invokeWithTarget:] + 64",
"22 CoreFoundation ___forwarding___ + 976",
"23 CoreFoundation _CF_forwarding_prep_0 + 96",
"24 CoreFoundation __invoking___ + 148",
"25 CoreFoundation -[NSInvocation invoke] + 428",
"26 ViewBridge __deferNSXPCInvocationOntoMainThread_block_invoke + 120",
"27 ViewBridge __wrapBlockWithVoucher_block_invoke + 56",
"28 ViewBridge kNotRunningOnAppKitCompatibleThread_block_invoke + 360",
"29 CoreFoundation __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 28",
"30 CoreFoundation __CFRunLoopDoBlocks + 364",
"31 CoreFoundation __CFRunLoopRun + 2432",
"32 CoreFoundation CFRunLoopRunSpecific + 612",
"33 HIToolbox RunCurrentEventLoopInMode + 292",
"34 HIToolbox ReceiveNextEventCommon + 648",
"35 HIToolbox _BlockUntilNextEventMatchingListInModeWithFilter + 76",
"36 AppKit _DPSNextEvent + 636",
"37 AppKit -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 716",
"38 ViewBridge __77-[NSViewServiceApplication vbNextEventMatchingMask:untilDate:inMode:dequeue:]_block_invoke + 136",
"39 ViewBridge -[NSViewServiceApplication _withToxicEventMonitorPerform:] + 152",
"40 ViewBridge -[NSViewServiceApplication vbNextEventMatchingMask:untilDate:inMode:dequeue:] + 168",
"41 ViewBridge -[NSViewServiceApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 100",
"42 AppKit -[NSApplication run] + 464",
"43 AppKit NSApplicationMain + 880",
"44 libxpc.dylib _xpc_objc_main + 976",
"45 libxpc.dylib xpc_main + 108",
"46 Foundation +[NSXPCListener serviceListener] + 0",
"47 PlugInKit pkSafeDataFromRelativeURL + 33800",
"48 PlugInKit pkSafeDataFromRelativeURL + 32752",
"49 PlugInKit pkSafeDataFromRelativeURL + 34680",
"50 ExtensionFoundation EXExtensionMain + 268",
"51 Foundation NSExtensionMain + 204",
"52 dyld start + 2236"
), com.apple.ViewBridge.error.description=NSViewBridgeErrorServiceBootstrap}
error 23:24:30.455372+0900 Finder FP Custom action sheet failed to load with error Error Domain=com.apple.ViewBridge Code=14 "(null)" UserInfo={com.apple.ViewBridge.error.hint=-[NSViewServiceMarshal bootstrap:withReply:] caught NSInternalInconsistencyException 'attempting to send message to non-existent action extension view controller' with backtrace (
<same backtrace as above>), com.apple.ViewBridge.error.description=NSViewBridgeErrorServiceBootstrap}