Thanks, @yonatan. Unfortunately, I note that discourse doesn’t allow me to update that post anymore.
I will add, because I saw earlier in this thread that I had expressed not having an example to point to for having worked out file uploads beyond the one example in the Binder Gallery of rendering an STL file, that now I did eventually figure out coding in general file uploading and subsequent use of that file for Voila. (Well at least single files.) Folks looking for more on that can see the links here.