I'm working with a digitizing program that is sensitive to ALT+TAB.
The digitizing process takes several hours.
And I would like to spend this time playing Heroes.
Therefore, I need windowed mode.

Tribes of the East version 3.0, official version.
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I changed setvar gfx_fullscreen = 1
to setvar gfx_fullscreen = 0

in

"D:\Games\heroes5orda\Heroes of Might and Magic V - Tribes of the East\profiles\default_profile\user_a2.cfg"

and assigned it in

"D:\Games\heroes5orda\Heroes of Might and Magic V - Tribes of the East\profiles\autoexec_a2.cfg"

It didn't help.

I reverted it back to
setvar gfx_fullscreen = 1

now I have windowed mode… :)