Unless I don't see it, there is no quit option, and alt+f4 seems to make the game crash whenever I use it. No issue with save corruption (so far), but it definitely feels unintentional, lol.
Oh, did I forget about something so basic as a quit game button? I will go add that to the list.
About the -crash- on shutdown. It's a know issue that shutdown times are astronomical (I have no clue why this happens, it seems to be engine related). I tend to use the command-line starter personally (the other exe on desktop builds), and stop the program by closing that. Hopefully a future update to Godot will resolve the issue.