Hi Pierre,
That is unusual for a Mac (since Apple controls the OpenGL drivers and you can’t change them). Usually it happens on Windows where the user typically must download and install the OpenGL drivers (depending on their particular graphics card).
Also in this post Paul had the same issue (Error: Missing GL version) and he fixed it by selecting the high-performance GPU instead of integrated GPU. I had a look at your specs and it appears you also have a dual-GPU setup (it mentions a AMD Radeon R9 M370X and a Intel Iris Pro with automatic graphics switching).
I just saw your latest post now. For a mid-2015 Macbook it should be no problem. You should be getting OpenGL 2.1 minimum. Actually I can see that’s what you’re getting which should be enough for GPlates, so there’s something else going on. It might still be a dual-GPU issue. If you could somehow manually switch to the AMD GPU then it might work - but I’m not sure how/if you can do that on macOS.