Tried it again with your original file - no editing of sketches and Sketch001 outside of Body.
Activating Body by double-clicking, select face on screen and the bend-line on screen (not Sketch001 in ComboView),
FoldWall-function is activ and the fold is created. (same behavior as described by Shalmeneser)
FC warns about the Sketch001:
PartDesign::FeaturePython: Link(s) to object(s) 'Sketch001' go out of the allowed scope 'Fold'. Instead, the linked object(s) reside within 'N/A'.
Fold is then an element of Body and Sketch001(now subelement of Fold) is moved into Body also.
At least I could replicate the behavior you are asking for: you do not use the command FoldWall, you press the button for command MakeWall
see screenshots, which button I'm using and the resulting fold.
Is this the fold you are looking for? Parameters of Fold can be altered in ComboView
about tree-view:
https://wiki.freecadweb.org/Tree_view