When viewing Resources in the left-hand column, I clicked the "+" button, selected "From Local" in the drop down, navigated the file explorer pop-up to my file, clicked "Open". At that point, my file showed up in the list resources, but with zeros (0) marked in the fields for width, height, andtotal bytes.
I don't find a Save/Upload button.
Possibly important info, I'm using Google Chrome version 80.0.3987.106 and Signage Studio online version 6.2.22.