I think we are talking about Windows app behavior, no?
In my experience pressing the X button on Windows usually closes the app entirely unless a setting specifies otherwise. I also find it annoying that Enpass minimizes to the tray when I click the X. The other thing that I find annoying is that if I then right click on the tray icon to close the app that way it loads another UI which I then need to click another "hamburger" style menu and then close the application down that way.
This could just be me and a couple others being stuck in our ways but this is fairly frustrating for some. Please at least give us an option to have the app fully close and not minimize to the system tray. There are a lot of programs out there that have this setting in their configuration. It's very common.
If I do not manually close Enpass each time, my sync software does not sync the files between my devices as it says the files which need to be synced are in use. This adds to my annoyance of the issue. It would be very nice to have an option to just have the app close when the X is clicked.