Slow load on simple application startup followed by "loading icon" over mouse

[<test_account tutanota de>]

Hi, I develop under windows with gtkmm...
I noticed when starting gtkmm application there is an "loading" icon showing next to mouse icon every time I run an executable.
The executable load is pretty slow hence the icon.

What can I do about this? is there anything to improve load time in order to get rid of the icon?
BTW: this icon only shows when running applications compiled with gtkmm, even "hello world window" if affected.

Thank you!