how to keep the window in position in the preview screen, when i resize it on the desktop?

[senseilance]

Hi; i try to not resize the window but sometimes it happens ... please advise TIA

 

[Suslik V]

OBS has no control over the external windows.
But the Source size can be fixed in OBS. You need Edit Transform (Ctrl+E) over the selected source and change the Bounding Box Type setting.