I received an assembly that was saved as a STEP file. When I open it and save it as a SW Assembly, the elements in the feature manager look like in the picture. Eventhough it's an assembly, I can't float any of the elements or apply mates to them. Any thoughts on what I could do?
that is the new 3D interconnect functionality.
you can either turn it off in settings before importing the step file or with it open as you show, right click at the top of the tree and choose dissolve - this will break the link to the step file.
But even after I do, I can float the whole main assembly, but all the subassemblies are still fixed and don't show me the option to float them
the component you have selected is within a sub-assembly - you need to be editing the sub-assembly to make changes at that level.
Did you try to move the hierarchy?
2018 SOLIDWORKS Help - Editing Assembly Structure
SOLIDWORKS - Breaking Down and Creating Subassemblies - YouTube
...as you have already imported with 3D Interconnect,.. I would save as Parasolid.. (x_t) then open/import the x_t.
that is the new 3D interconnect functionality.
you can either turn it off in settings before importing the step file or with it open as you show, right click at the top of the tree and choose dissolve - this will break the link to the step file.