The Wolfram Language Introductory Book, chapter 44 Importing and Exporting, gives an example of exporting 3D geometry in a format suitable for 3D printing. I copied the example to my notebook.

Export["spikey.stl",Entity["Polyhedron","RhombicHexecontahedron"]["Image"]]

But when I run it I get the error message Export: Image cannot be exported to the STL format.

If I change the file name to Spikey.pdf it exports OK to a pdf file.

I ran $ExportFormats and STL is listed as a format for my session.

I can view it OK by just using

Entity["Polyhedron","RhombicHexecontahedron"]["Image"]

and I tried exporting with and without the "Image" included.

I tried a simple object, a Tetrahedron, but same results. It seems odd it doesn't work straight out of the "official" introductory book.

My Mathematica is version 12.0 and is running on a Raspberry Pi Linux system.

Any suggestions ?