I think the correct solution here should be to get AppKit to recognize our fullscreen menu item as the legitimate one, rather than using the user default to suppress the addition of the second one in the Window menu.

I've force-re-submitted an improved commit based on the above feedback, though honestly @low-batt should get full credit, since he did do more than 50% of the work for this one-liner.

I think the correct solution here should be to get AppKit to recognize our fullscreen menu item as the legitimate one, rather than using the user default to suppress the addition of the second one in the Window menu.

@saagarjha I did a deep-dive into this...

Of the affected open source projects I found, the majority seem to have settled on the above preference setting (Electron being the biggest name I found) but I did discover that the Chromium was able to trigger Apple's matching logic by changing the name of the menu item action to toggleFullScreen and is using that.

I was able to do the same in this branch, but there are still some problems. I was only able to trigger the override by hard-coding the action selector in the XIB file. But I still can't figure out how to create a selector for MainWindowController inside the XIB -- IINA is currently doing that in code after the app has started. Best I could do was to make the XIB call an action in MenuController, which in turn calls the action in MainWindowController. And everything works this way - except the "Enter Full Screen" menu item is never grayed out because it's using a MenuController selector instead of a MainWindowController selector, and I'm not ready to commit a lot more time to figure out how to make that work.

IMHO it seems like using a special selector name is not the most robust solution, especially because I haven't found any documentation from Apple to support it. At least the preference key is documented.

@svobs Full credit goes to you for providing the implementation. With Apple specifying a clear requirement on how the menus must be structured, but apparently no documentation on how to implement it, I thought this needed a detailed review.

Due to the feedback from @saagarjha I looked again for guidence from Apple on how to implement the HIG requirement of suppressing the menu item in the Window menu. Nothing useful.

One reason why developers fail to document things is because "it is obvious". So I tried a quick experiment. I first made sure to delete the preference:

defaults delete com.colliderli.iina NSFullScreenMenuItemEverywhere

The documentation for NSWindow.toggleFullScreen says:

If an application supports fullscreen, it should add a menu item to the View menu with toggleFullScreen: as the action, and nil as the target.

IINA's main menu does not contain a "Enter Full Screen" menu item. In a quick test I added that menu item to the Window menu and tied the action to toggleFullScreen in First Responder and checked Hidden. That quick test seemed to work. Busy today, so I only tested Monterey.

Given the only documentation for NSFullScreenMenuItemEverywhere is from that archived old AppKit release notes from 10.12, maybe adding a menu item as a solution should be further explored?

I followed this post in order to properly attach the action:
How to connect IBAction and menu item to First Responder?

If the menu item action is not attached to toggleFullScreen then AppKit does not recognize it as the standard Enter Full Screen menu item.

My understanding is that using the toggleFullScreen: action is the correct way to do this, yes. Is it not being propagated correctly through the responder chain?

The responder chain is not being used. The full screen menu item under the Video menu is tied to MenuController which sets the action to MainWindowController.menuToggleFullScreen. That calls the method toggleWindowFullScreen which will either call NSWindow.toggleFullScreen or legacy full screen methods in MainWindowController.

The task at hand is to eliminate the full screen menu item under the Window menu. Right now IINA does not have such a menu item. AppKit is adding a disabled one. By adding a full screen menu item under the Window menu, using NSWindow.toggleFullScreen and marking that menu item as hidden we can eliminate the disabled Enter Full Screen as required by the HIG.