Desktop app lifecycle
What follows applies only to the installed desktop app. In the browser there is no program window to close, and no installer to update.
Closing the program with unsaved changes
Closing the window of a modified plan triggers a confirmation prompt: confirming closes the window, cancelling leaves the plan open.
Updates
When the main instance starts, the app checks for a new version — this can be turned off under Settings, group Updates. If there is one, an information bar appears at the top, whose urgency distinguishes between a regular, a significant, and a security-relevant update. You can open the new version, ignore just this one version, or dismiss the bar. Which channel is checked, Stable, Beta, or Alpha, is set in the same group.
Opening files from the operating system
Opening a plan file from Explorer, Finder or a Linux file manager, by double-clicking or "Open with", starts it in a new window — unless the app was not open at all yet, in which case it fills that first window. A file that is not a plan but is importable (STL, 3MF, an image …) instead lands in the currently open window, just as with import from the menu.