https://bugs.winehq.org/show_bug.cgi?id=46376
--- Comment #1 from Ken Thomases ken@codeweavers.com --- (In reply to Andrew Fan from comment #0)
Regarding this part:
Worse, it was difficult to replicate because a freeze during fullscreen mode required forcefully killing the OS and rebooting the machine since all other I/O other than hard reset are blocked by Wine.
That shouldn't be the case, unless Wine provoked a kernel hang or GPU restart or something like that (which is, ultimately, a OS bug; no matter what Wine does, it shouldn't be able to lock up the system like that).
If Wine has frozen up while in full-screen mode, a simple Command-Tab might work to get out of it. Wine's main thread is dedicated to Cocoa stuff and is usually not caught up in a hang of the Windows program. And that main thread is what gets you out of full-screen mode on a Command-Tab.
If that doesn't work, the main thread may be stuck, too. Less common, but does happen. Even so, though, you should be able to Force Quit it using the system-wide Force Quit keyboard shortcut: Command-Option-Escape, possibly followed by Return twice.