I have read other answers to this question and have checked “Keep Xojo running” in the Edit > Options but still no success. I see that Xojo still runs in the system tray but this does not solve the issue. Is this a bug and can it be fixed?
What platform are you using. As far as I can remember that is normal behaviour for Windows programs.
If you see the Xojo icon in the tray area then that checkbox is doing its job correctly and Xojo is still running.
The question is, though, how do you then get Xojo (whose only visible presence is then the icon in the tray) to present the “Choose a Project” panel? Or do you just click the icon?
I’m not at a PC to test right now but I’m pretty sure there’s a menu when you click the icon.
You need to contextual click the icon to get the menu.
Thank you for responding! I am on Windows 11 and have a PC. I’m not an expert, but from my experience, projects in other IDEs can be closed without the IDE itself closing.
OK - so do you see the Xojo icon in the tray? What happens if you right-click it?
Thank you - yes, the icon is greyed out but when clicked it does open in a new project. So I guess I’ll have to get used to it. I just wondered what the purpose of the “Close Window” button in the menu is, I thought it meant “Close Project”. Thank you very much for all your kind responses, much appreciated! 
You can have more than one window open within Xojo at the same time, even on a single project.