Well I tried to reproduce the problem Win 11 / Gimp 2.0.4 without success. From your video 1920 x 1020 so a HD display ? and probably more relevant it look like F11 used to get a full screen Gimp window. One problem with windows is there is only a close icon for those dialogue windows, no max or min icons. I have the full set In linux for min / max so no problem. More a Windows than Gimp problem.
FWIW my advice is:
F11 to toggle out of full window mode
then
Edit -> Preferences -> Interface -> Window Management and click on Reset Saved Window Positions to Default Values.
Restart Gimp and try again.
That bug report, I think is this one https://gitlab.gnome.org/GNOME/gimp/-/issues/14125 The title looks promising "Save as" dialog has larger height than desktop viewport but the issue was closed because the report is garbled. You might want to start a new better one.
FWIW my advice is:
F11 to toggle out of full window mode
then
Edit -> Preferences -> Interface -> Window Management and click on Reset Saved Window Positions to Default Values.
Restart Gimp and try again.
That bug report, I think is this one https://gitlab.gnome.org/GNOME/gimp/-/issues/14125 The title looks promising "Save as" dialog has larger height than desktop viewport but the issue was closed because the report is garbled. You might want to start a new better one.