OK, I think I am good now. I can get two (or more) stl files imported into SuperSlicer but not via the SS import function. I can however go into the file manager, select two (or more) files with the help of the ctrl key and then drag both of them into SuperSlicer. The very first thing in SuperSlicer that needs to be done is to 'merge' the two files in order to be able to manipulate te object without messing up the positions of the components relative to each other.
Once a part of the object has been moved relative to other parts, I can not get the parts to reposition themselves back to the original positions relative to each other.
In Fusion360, I can generate a single 3mf file that contains all the parts of the multi part model by making all the individual components/parts visible, then selecting the top level part and selecting 'save as mesh' followed by '3mf' format. I can then drag the 3mf file, which contains all sub parts, into SuperSlicer. Again, the very first thing that needs doing is to 'merge' the sub parts so that the object can be manipulated as one (foe example to locate the right face onto the build plate). If the sub parts are not merged and are moved relative to each other, I have not found a way to restore the original positions.
Merging is done on the right side of the SuperSlicer screen by selecting all the sub parts, right clicking and selecting 'merge'. If moving the combined merged object, make sure only the merged object is selected as the individual parts, if selected, could be moved relative to each other which would screw things up.
I have yet to see the screen where SuperSlicer asks me if individual parts should be considered one object.
I am moving on from trying to get the object into SuperSlicer to hopefully printing a multi colour model.
Thanks for the help!