I used this one in 2022 to make a proof of concept for a build once / run anywhere graphical app and IIRC the library was quite nice, even if a bit limited. The resulting kludge is at https://github.com/jacereda/cosmogfx and there's a prebuilt binary that should run on Linux, Windows and some BSDs. https://github.com/jacereda/cosmogfx/releases/download/v0.0....

Cosmopolitan Libc has since integrated the bits to make OpenGL work in cross-platform binaries and it's awesome.