Just came across this news report
about the Smithsonian Institution making a whole bunch of stuff
available for free download and reuse under a Creative Commons CC0
More info on their home page <https://www.si.edu/OpenAccess>.
I had a quick look at one or two 3D models from
<https://3d.si.edu/cc0>, and I see OBJ, glTF (OpenGL Transfer Format)
and GLB (binary version of glTF) options available. These are all open
formats, well-supported in non-proprietary software.