Second reply -- if anyone wants to run Dune3D, flatpak or compiled, they must set this flag in advance:

export GDK_DEBUG="gl-prefer-gl"

I discovered this while trying out the compiled version (it's essential for the program to run at all), and for some reason I thought the FlatPak install would have done away with this oddity.

Again, because my students aren't necessarily techies, this kind of hacking shouldn't exist in a program released to mere mortals.

But thanks again for alerting me to this release version.

Thanks -- I missed this. If it pans out, it might get me to shift away from SolveSpace, which has a few perpetually annoying quirks.