Solved

Standalone version can't do windowed mode or quit

What did you try to do?
Change it to windowed mode

What happened instead?
Clicked on settings, changed to windowed mode, saved. Went back to settings still says fullscreen. And after cache clear too. Also there is no button anywhere to close the app.

Did the problem happen while using wi-fi, mobile data, or both?
Wi-fi

Did the bug happen in the app, on PC, or both?
PC

What operating system is your PC?
Windows

Which browser did you experience the problem in?
Standalone

Can the bug be reproduced?
Yes

Additional comments:

iGP Manager screen press ALT+Enter changed screen size and give you bar at top to close program this is on a windows 10.

Thanks Colin, that worked. I still think this should be possible through the game settings though, as it defaults to full screen and unless you know this key combo (or Alt-F4) then you are stuck.

glad I could help.