It targets OpenGL 2.1, I am hoping to move it forward to the OpenGL 3.3 core profile and GLSL 1.50 (if memory serves) soon. This is well supported on macOS, Linux, and Windows by most modern cards (and has been the minimum in VTK for 2+ years now (I think, didn’t verify but from memory/roughly).
We use QOpenGLWidget in Avogadro 2 master, and also in VTK. Please look at master, and I will push a new release out soon as I think it is important to get that tested by more people. A release is overdue at this point.