Is there a way to save a polygon as another file type, like .tif?
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You can create a map containing any layer (including polygons) and Export it as a .TIF (or .JPG, or .PDF) by opening the File menu and choosing Print/Publish Maps.
That said, if you are looking to export the polygon as a GPX, KML/KMZ, Shapefile, or similar format, that is a different matter (and would be a different feature to request,)