The boundary conditions on the FBD tab are static conditions. These are used to localize the design-to loads into the objects based on plate theory assumptions and strain compatibility. For many aerospace applications, such as wing skins and cylindrical panels between ring frames, the static boundary conditions are "fixed" at the +X, -X edges. If you observe the static deformation of these panels, the panels have zero rotation above the frames. See attached image. The blue dashed line shows the static deformation. Notice the fixed condition over the frames.
The boundary conditions on the buckling tab are buckling boundary conditions. These conditions do not affect the stress analysis or local buckling analysis. These conditions are input into the panel buckling analysis. The same wing skin and cylindrical panels with "fixed" static boundary conditions will have "simple" buckling boundary conditions. The buckling mode shapes will alternate between bays. One bay will buckle up and the adjacent bay will buckle down. So, there is a pinned condition where the frames connect to the skin. See attached image. The green dashed line shows the buckling deformation. Notice the "pinned" or "simple" condition at the frames.
