This is FUD. There isn't a single real desktop Linux distribution without OpenGL support. The basic OpenGL API hasn't changed ever, it's just been extended. It has even more backwards compatibility than Direct3D. Sure you can deliberately build a distro with only Vulkan or GLES (a mobile API) if you want to be an ass but the same goes for Windows. Same for X11 - Xlib works everywhere even any Wayland-only distribution that gives a single crap about running binary distributed software.

Now GUI toolkits are more of an issue. That's annoying for some programs, many others do their own thing anyway.