the window I would gladly keep open, but it closes after the timeout of 30 seconds and even before sometimes.
Please re-read my reply again: I wasn't referring to the menu windows, but the GSX toolbar icon.
If you read the manual at Pages 66-67 as I've asked to do, it explains the different from having the Toolbar icon Active or Inactive, and why GSX sometimes close it automatically and why it doesn't, and when it doesn't, it's because you are in the middle of some procedure (Refueling is one of such cases), where you are supposed to keep it Active (with the menu closed! ), so the menu can be reopened again automatically when it need to perform the next step, which would be asking the fuel quantity.
Hello how to select the turn type short/long/manual i don't have it in my FMC 737 PMDG MSFS
That's the only page of the whole manual that hasn't been rewritten from the P3D version. In the PMDG for MSFS, you just select the Fuel from the Fuel page, but the principle is the same.
However, this begin a plane using a custom fuel system, there's no GSX menu that is supposed to open automatically, just a voice (and a message, if the toolbar icon is active) telling you when load the fuel in the airplane own menu.