Last year Steve Endow did a post on Microsoft Dynamics GP 2018 always starts full screen and how you can stop it from doing so. The cause is a setting in the Dex.ini file which was set to TRUE:
WindowMax=TRUE
Prior versions of Dynamics GP had this setting set to FALSE; at the time he posed, Steve wasn’t sure if the setting was always set to TRUE or only if the Web Client Runtime was installed. Well, I can confirm that it is always set to TRUE.
I haven’t been that bothered by Dynamics GP always starting full screen, but after a client upgrade I was asked by them about it.
To stop Dynamics GP always starting full screen you need to change the Dex.ini file setting to false; this needs to be done on every client. If you are a GP Power Tools user you can use the Dex.ini Configuration tool to change all clients, otherwise you will need to manually update all clients.