I thought "yes", but just tested and turns out it's more like "kinda". It doesn't do a full sync on shutdown, but if something is modified it sends a sync push , and that change will get picked up after a few seconds. So if you have a note that you modify, and then allow a few seconds, and then close...That modification will show up on other devices outside of a full sync.

But you can't open joplin, create a note, and then immediately exit and expect the note to show up on other devices. It will still exist on the device it was created on, so it's not lost, it just hasn't synced yet. It will automatically sync the next time you start joplin though.

In my case, I use the vim key bindings, and am so accustomed to hitting "<esc>:w" (which does perform a sync) when I'm finished writing the note, I never noticed.