In the MacOS ChatGPT app, closing the chat window puts the user in a non-intuitive state.
If they hit Cmd-N or Cmd-Shift-N to start a new chat, nothing happens, as the chat window is gone.
If the user quits the app and restarts, the window comes back and all is well (until the user hits Cmd-W again).
After several tries, I found the “ChatGPT” menu item in the Window menu (which is bound to Cmd-1).
Cmd-1 works, but I really had to search.
I’d recommend hitting Cmd-N or Cmd-Shift-N when there is no window just make a chat window visible, as there’s no other reason the user would invoke Cmd-N/Cmd-Shift-N.
Apologies if there was a better place to file this bug - after several ChatGPT queries, this is where I landed.