But i finally found the solution (thanks to ChatGPT 🙂 ).
#include <WinAPI.au3>
;Just for where the $hGui variable is:
;Local $hGui=GUICreate("Welcome", $xSize, $ySize, 100, 100, BitOR($WS_SYSMENU,$WS_POPUP), 0)
_WinAPI_ShowWindow($hGui, @SW_HIDE) ; Hide the window
_WinAPI_SetWindowLong($hGui, $GWL_EXSTYLE, BitOR(_WinAPI_GetWindowLong($hGui, $GWL_EXSTYLE), $WS_EX_TOOLWINDOW)) ; Set the window as a tool window
WinSetState($hGui, "", @SW_HIDE) ; Hide the window from the taskbar
Iam so happy 🙂