The title bar with minimize, maximize and restore buttons can be hidden by passing "--show fullscreen" command line parameter when launching the app.
C:\Users\username\Applications\ArcGIS\MyApp\MyApp.exe --show fullscreen
Other possible command line values are,
--show maximized ( Shows the window as maximized.)
--show minimized ( Shows the window as minimized.)
--show normal ( Shows the window as normal, i.e. neither maximized, minimized, nor fullscreen.)
Currently the maximized mode is used when "Full Screen" setting is enabled in AppStudio Settings tool. This will be fixed to use the "--show fullscreen" mode in next AppStudio update( scheduled for release towards end of next month).
For those who might try this in the interim before next release, note that for this to work you need to set the 'Full Screen mode' in the AppStudio settings tool to disabled.
Just a follow up to this thread from a couple of months back.
I see that in AppStudio now (v1.2), as you mentioned, the 'Full Screen' setting now uses the '--show fullscreen' mode. However, since there appears to be four standard 'options', so to speak, (fullscreen, maximised, minimised and normal), it would be great if, in a future AppStudio update, the 'Full Screen' toggle switch be changed to a radio button with those four options.
Typically, I would use either 'Full Screen' or 'Maximised', but it would make sense to expose all four options.